diff --git a/Assets/Scripts/Building.cs b/Assets/Scripts/Building.cs
index eab42ac..ab6f893 100644
--- a/Assets/Scripts/Building.cs
+++ b/Assets/Scripts/Building.cs
@@ -5,7 +5,7 @@ using Northbound.Data;
 
 namespace Northbound
 {
-    public class Building : NetworkBehaviour, IDamageable, IVisionProvider, ITeamMember, IHealthProvider
+    public class Building : NetworkBehaviour, IDamageable, IVisionProvider, ITeamMember, IHealthProvider, IInteractable
     {
         [Header("References")]
         public TowerData buildingData;
@@ -66,6 +66,26 @@ namespace Northbound
         private UnitHealthBar _healthBar;
         private float _lastRegenTime;
 
+        // 업그레이드 관련
+        private NetworkVariable<bool> _isUpgrading = new NetworkVariable<bool>(
+            false,
+            NetworkVariableReadPermission.Everyone,
+            NetworkVariableWritePermission.Server
+        );
+        private NetworkVariable<float> _upgradeProgress = new NetworkVariable<float>(
+            0f,
+            NetworkVariableReadPermission.Everyone,
+            NetworkVariableWritePermission.Server
+        );
+        private NetworkVariable<int> _upgradeTargetId = new NetworkVariable<int>(
+            0,
+            NetworkVariableReadPermission.Everyone,
+            NetworkVariableWritePermission.Server
+        );
+
+        private float _lastInteractionTime;
+        private const float INTERACTION_COOLDOWN = 0.5f;
+
         public override void OnNetworkSpawn()
         {
             base.OnNetworkSpawn();
@@ -108,6 +128,8 @@ namespace Northbound
             // 이벤트 구독
             _currentHealth.OnValueChanged += OnHealthValueChanged;
             _team.OnValueChanged += OnTeamValueChanged;
+            _upgradeProgress.OnValueChanged += OnUpgradeProgressChanged;
+            _isUpgrading.OnValueChanged += OnUpgradingChanged;
 
             // 체력바 생성
             if (showHealthBar && healthBarPrefab != null)
@@ -124,6 +146,8 @@ namespace Northbound
         {
             _currentHealth.OnValueChanged -= OnHealthValueChanged;
             _team.OnValueChanged -= OnTeamValueChanged;
+            _upgradeProgress.OnValueChanged -= OnUpgradeProgressChanged;
+            _isUpgrading.OnValueChanged -= OnUpgradingChanged;
 
             // FogOfWar 시스템에서 제거
             if (IsServer && buildingData != null && buildingData.providesVision)
@@ -480,6 +504,265 @@ namespace Northbound
 
         #endregion
 
+        #region IInteractable Implementation (Upgrade)
+
+        /// <summary>
+        /// 상호작용 가능 여부
+        /// </summary>
+        public bool CanInteract(ulong playerId)
+        {
+            // 쿨다운 확인
+            if (Time.time - _lastInteractionTime < INTERACTION_COOLDOWN)
+                return false;
+
+            // 같은 팀만 업그레이드 가능
+            TeamType team = GetPlayerTeam(playerId);
+            if (team != _team.Value)
+                return false;
+
+            // 업그레이드 중이면 진행 가능
+            if (_isUpgrading.Value)
+                return true;
+
+            // 업그레이드 시작 가능 여부 확인
+            if (buildingData == null || buildingData.upgradeTo == 0)
+                return false;
+
+            TowerData upgradeData = GetUpgradeData();
+            if (upgradeData == null)
+                return false;
+
+            // 자원이 충분한지 확인
+            var coreResourceManager = CoreResourceManager.Instance;
+            if (coreResourceManager == null || !coreResourceManager.CanAfford(upgradeData.mana))
+                return false;
+
+            return true;
+        }
+
+        /// <summary>
+        /// 상호작용 실행 (업그레이드)
+        /// </summary>
+        public void Interact(ulong playerId)
+        {
+            if (!CanInteract(playerId))
+                return;
+
+            // 서버에 업그레이드 요청
+            RequestUpgradeServerRpc(playerId);
+        }
+
+        [Rpc(SendTo.Server)]
+        private void RequestUpgradeServerRpc(ulong playerId)
+        {
+            if (!CanInteract(playerId))
+                return;
+
+            _lastInteractionTime = Time.time;
+
+            // 업그레이드가 시작되지 않았으면 시작만 하고 종료
+            if (!_isUpgrading.Value)
+            {
+                TowerData upgradeData = GetUpgradeData();
+                if (upgradeData == null)
+                    return;
+
+                // 자원 확인 및 소비
+                var coreResourceManager = CoreResourceManager.Instance;
+                if (coreResourceManager == null || !coreResourceManager.CanAfford(upgradeData.mana))
+                    return;
+
+                coreResourceManager.SpendResources(upgradeData.mana);
+
+                // 업그레이드 시작 - 토대로 교체
+                StartUpgradeToFoundation(upgradeData);
+                return;
+            }
+
+            // 이미 업그레이드 중이면 플레이어의 manpower만큼 진행
+            float playerManpower = GetPlayerManpower(playerId);
+            _upgradeProgress.Value += playerManpower;
+
+            // 완료 체크
+            TowerData targetData = BuildingManager.Instance?.GetTowerDataById(_upgradeTargetId.Value);
+            if (targetData != null && _upgradeProgress.Value >= targetData.manpower)
+            {
+                CompleteUpgrade(targetData);
+            }
+        }
+
+        /// <summary>
+        /// 업그레이드 시작 - 건물을 토대로 교체
+        /// </summary>
+        private void StartUpgradeToFoundation(TowerData upgradeData)
+        {
+            if (!IsServer) return;
+            if (BuildingManager.Instance == null) return;
+            if (BuildingManager.Instance.foundationPrefab == null) return;
+
+            // 현재 건물 정보 저장
+            Vector3Int gridPos = gridPosition;
+            int rot = rotation;
+            ulong owner = _ownerId.Value;
+            TeamType team = _team.Value;
+
+            // BuildingManager에서 건물 제거
+            BuildingManager.Instance.RemoveBuilding(this);
+
+            // FogOfWar 시스템에서 제거
+            if (buildingData != null && buildingData.providesVision)
+            {
+                FogOfWarSystem.Instance?.UnregisterVisionProvider(this);
+            }
+
+            // 현재 건물 제거
+            NetworkObject.Despawn(true);
+
+            // 토대 생성
+            Vector3 worldPosition = BuildingManager.Instance.GridToWorld(gridPos);
+            GameObject foundationObj = Instantiate(BuildingManager.Instance.foundationPrefab, worldPosition + upgradeData.placementOffset, Quaternion.Euler(0, rot * 90f, 0));
+            NetworkObject foundationNetObj = foundationObj.GetComponent<NetworkObject>();
+
+            if (foundationNetObj != null)
+            {
+                foundationNetObj.Spawn();
+
+                BuildingFoundation foundation = foundationObj.GetComponent<BuildingFoundation>();
+                if (foundation != null)
+                {
+                    foundation.Initialize(upgradeData, gridPos, rot, owner, team);
+                    BuildingManager.Instance.RegisterFoundation(foundation);
+                }
+            }
+            else
+            {
+                Destroy(foundationObj);
+            }
+        }
+
+        /// <summary>
+        /// 업그레이드 완료
+        /// </summary>
+        private void CompleteUpgrade(TowerData upgradeData)
+        {
+            if (!IsServer) return;
+
+            BuildingManager.Instance?.UpgradeBuilding(this, upgradeData);
+        }
+
+        /// <summary>
+        /// 상호작용 프롬프트 텍스트
+        /// </summary>
+        public string GetInteractionPrompt()
+        {
+            // 업그레이드 중이면 진행도 표시
+            if (_isUpgrading.Value)
+            {
+                TowerData targetData = BuildingManager.Instance?.GetTowerDataById(_upgradeTargetId.Value);
+                if (targetData != null)
+                {
+                    float percentage = (_upgradeProgress.Value / targetData.manpower) * 100f;
+                    return $"[E] Upgrading to {targetData.buildingName} ({percentage:F0}%)";
+                }
+                return "[E] Upgrading...";
+            }
+
+            TowerData upgradeData = GetUpgradeData();
+            if (upgradeData == null)
+                return "";
+
+            var coreResourceManager = CoreResourceManager.Instance;
+            bool canAfford = coreResourceManager != null && coreResourceManager.CanAfford(upgradeData.mana);
+
+            string costText = canAfford ? $"{upgradeData.mana}" : $"<color=red>{upgradeData.mana}</color>";
+            return $"[E] Upgrade to {upgradeData.buildingName} ({costText})";
+        }
+
+        public string GetInteractionAnimation()
+        {
+            return "Build"; // 건설 애니메이션 재사용
+        }
+
+        public EquipmentData GetEquipmentData()
+        {
+            return buildingData?.constructionEquipment;
+        }
+
+        Transform IInteractable.GetTransform()
+        {
+            return transform;
+        }
+
+        /// <summary>
+        /// 업그레이드 대상 TowerData 반환
+        /// </summary>
+        public TowerData GetUpgradeData()
+        {
+            if (buildingData == null || buildingData.upgradeTo == 0)
+                return null;
+
+            if (BuildingManager.Instance == null)
+                return null;
+
+            return BuildingManager.Instance.GetTowerDataById(buildingData.upgradeTo);
+        }
+
+        /// <summary>
+        /// 플레이어의 팀 가져오기
+        /// </summary>
+        private TeamType GetPlayerTeam(ulong playerId)
+        {
+            if (NetworkManager.Singleton != null && NetworkManager.Singleton.ConnectedClients != null)
+            {
+                if (NetworkManager.Singleton.ConnectedClients.TryGetValue(playerId, out var client))
+                {
+                    if (client.PlayerObject != null)
+                    {
+                        var teamMember = client.PlayerObject.GetComponent<ITeamMember>();
+                        if (teamMember != null)
+                        {
+                            return teamMember.GetTeam();
+                        }
+                    }
+                }
+            }
+            return TeamType.Player;
+        }
+
+        /// <summary>
+        /// 플레이어의 manpower 가져오기
+        /// </summary>
+        private float GetPlayerManpower(ulong playerId)
+        {
+            if (NetworkManager.Singleton != null && NetworkManager.Singleton.ConnectedClients != null)
+            {
+                if (NetworkManager.Singleton.ConnectedClients.TryGetValue(playerId, out var client))
+                {
+                    if (client.PlayerObject != null)
+                    {
+                        var playerInteraction = client.PlayerObject.GetComponent<PlayerInteraction>();
+                        if (playerInteraction != null)
+                        {
+                            return playerInteraction.WorkPower;
+                        }
+                    }
+                }
+            }
+            return 10f; // 기본값
+        }
+
+        private void OnUpgradeProgressChanged(float oldValue, float newValue)
+        {
+            // 업그레이드 진행 UI 업데이트 (필요시 구현)
+        }
+
+        private void OnUpgradingChanged(bool oldValue, bool newValue)
+        {
+            // 업그레이드 상태 변경 시 처리 (필요시 구현)
+        }
+
+        #endregion
+
         #region Gizmos
 
         private void OnDrawGizmos()
diff --git a/Assets/Scripts/BuildingManager.cs b/Assets/Scripts/BuildingManager.cs
index 20f8778..02c58e4 100644
--- a/Assets/Scripts/BuildingManager.cs
+++ b/Assets/Scripts/BuildingManager.cs
@@ -296,6 +296,17 @@ namespace Northbound
             }
         }
 
+        /// <summary>
+        /// 토대 등록 (업그레이드 등으로 생성된 토대)
+        /// </summary>
+        public void RegisterFoundation(BuildingFoundation foundation)
+        {
+            if (!placedFoundations.Contains(foundation))
+            {
+                placedFoundations.Add(foundation);
+            }
+        }
+
         /// <summary>
         /// 사전 배치 건물 등록 (씬에 미리 있는 건물용)
         /// </summary>
@@ -516,5 +527,91 @@ namespace Northbound
                 Destroy(buildingObj);
             }
         }
+
+        #region Upgrade System
+
+        /// <summary>
+        /// ID로 TowerData 찾기
+        /// </summary>
+        public TowerData GetTowerDataById(int towerId)
+        {
+            foreach (var data in availableBuildings)
+            {
+                if (data != null && data.id == towerId)
+                {
+                    return data;
+                }
+            }
+            return null;
+        }
+
+        /// <summary>
+        /// 건물 업그레이드 (서버에서만 호출)
+        /// </summary>
+        public void UpgradeBuilding(Building building, TowerData upgradeData)
+        {
+            if (!IsServer) return;
+            if (building == null || upgradeData == null) return;
+            if (upgradeData.prefab == null)
+            {
+                Debug.LogError($"[BuildingManager] 업그레이드 프리팹이 없습니다: {upgradeData.buildingName}");
+                return;
+            }
+
+            // 기존 건물 정보 저장
+            Vector3Int gridPos = building.gridPosition;
+            int rotation = building.rotation;
+            ulong ownerId = building.GetOwnerId();
+            TeamType team = building.GetTeam();
+
+            // 기존 건물 제거
+            placedBuildings.Remove(building);
+
+            // FogOfWar 시스템에서 제거
+            if (building.buildingData != null && building.buildingData.providesVision)
+            {
+                FogOfWarSystem.Instance?.UnregisterVisionProvider(building);
+            }
+
+            // 기존 건물 파괴
+            building.NetworkObject.Despawn(true);
+
+            // 새 건물 생성
+            Vector3 worldPosition = GridToWorld(gridPos);
+            GameObject newBuildingObj = Instantiate(upgradeData.prefab, worldPosition + upgradeData.placementOffset, Quaternion.Euler(0, rotation * 90f, 0));
+            NetworkObject netObj = newBuildingObj.GetComponent<NetworkObject>();
+
+            // FogOfWarVisibility 추가
+            if (newBuildingObj.GetComponent<FogOfWarVisibility>() == null)
+            {
+                var visibility = newBuildingObj.AddComponent<FogOfWarVisibility>();
+                visibility.showInExploredAreas = true;
+                visibility.updateInterval = 0.2f;
+            }
+
+            if (netObj != null)
+            {
+                netObj.SpawnWithOwnership(ownerId);
+
+                Building newBuilding = newBuildingObj.GetComponent<Building>();
+                if (newBuilding == null)
+                {
+                    newBuilding = newBuildingObj.AddComponent<Building>();
+                }
+
+                // 새 건물 초기화
+                newBuilding.Initialize(upgradeData, gridPos, rotation, ownerId, team);
+                placedBuildings.Add(newBuilding);
+
+                Debug.Log($"<color=green>[BuildingManager] 건물 업그레이드 완료: {upgradeData.buildingName}</color>");
+            }
+            else
+            {
+                Debug.LogError($"<color=red>[BuildingManager] 업그레이드 프리팹에 NetworkObject가 없습니다!</color>");
+                Destroy(newBuildingObj);
+            }
+        }
+
+        #endregion
     }
 }