diff --git a/DESIGN.md b/DESIGN.md
index edb018c..a02ea74 100644
--- a/DESIGN.md
+++ b/DESIGN.md
@@ -36,3 +36,47 @@ graph TD;
     C[RedisInventoryService] --> E[Redis Database];
     D[JSONFileInventoryService] --> F[JSON File];
 
+```
+
+### Sequence Diagram for ATM Operations
+Withdraw Money
+
+```mermaid
+sequenceDiagram
+    participant User
+    participant FastAPI
+    participant ATMService
+    participant InventoryService
+
+    User->>FastAPI: POST /atm/withdrawal
+    FastAPI->>ATMService: withdraw_money(amount)
+    ATMService->>InventoryService: acquire_lock()
+    InventoryService-->>ATMService: lock_acquired
+    ATMService->>InventoryService: read_inventory()
+    InventoryService-->>ATMService: inventory_data
+    ATMService->>InventoryService: write_inventory(updated_inventory)
+    ATMService->>InventoryService: release_lock()
+    ATMService-->>FastAPI: withdrawal_result
+    FastAPI-->>User: withdrawal_result
+
+```
+Refill Money
+
+```mermaid
+sequenceDiagram
+    participant User
+    participant FastAPI
+    participant ATMService
+    participant InventoryService
+
+    User->>FastAPI: POST /atm/refill
+    FastAPI->>ATMService: refill_money(money)
+    ATMService->>InventoryService: acquire_lock()
+    InventoryService-->>ATMService: lock_acquired
+    ATMService->>InventoryService: read_inventory()
+    InventoryService-->>ATMService: inventory_data
+    ATMService->>InventoryService: write_inventory(updated_inventory)
+    ATMService->>InventoryService: release_lock()
+    ATMService-->>FastAPI: refill_result
+    FastAPI-->>User: refill_result
+```
\ No newline at end of file