diff --git a/backend/tests/test_offline_sync.py b/backend/tests/test_offline_sync.py
new file mode 100644
index 00000000..cad4ab37
--- /dev/null
+++ b/backend/tests/test_offline_sync.py
@@ -0,0 +1,110 @@
+import pytest
+from fastapi import status
+from uuid import uuid4
+
+
+class TestOfflineSync:
+    """Test offline sync functionality."""
+
+    def test_sync_operations_with_uuid(self, test_client, test_db):
+        """Test that offline operations with UUIDs are tracked."""
+        from backend.models import Item
+
+        item = Item(
+            name="Test Item",
+            category="Electronics",
+            item_type="Component",
+            quantity=10,
+            barcode="123456789",
+            part_number="PN-12345"
+        )
+        test_db.add(item)
+        test_db.commit()
+
+        operation_uuid = str(uuid4())
+        response = test_client.post(
+            "/api/bulk-sync",
+            json={
+                "operations": [
+                    {
+                        "id": operation_uuid,
+                        "type": "CHECK_IN",
+                        "item_id": item.id,
+                        "quantity": 5,
+                        "timestamp": "2026-04-18T10:00:00Z"
+                    }
+                ]
+            }
+        )
+        assert response.status_code == status.HTTP_200_OK
+        assert response.json()["synced"] == 1
+
+    def test_sync_duplicate_uuid_ignored(self, test_client, test_db):
+        """Test that duplicate UUIDs don't create duplicate entries."""
+        from backend.models import Item, AuditLog
+
+        item = Item(
+            name="Test Item",
+            category="Electronics",
+            item_type="Component",
+            quantity=10,
+            barcode="123456789",
+            part_number="PN-12345"
+        )
+        test_db.add(item)
+        test_db.commit()
+
+        operation_uuid = str(uuid4())
+        operation = {
+            "id": operation_uuid,
+            "type": "CHECK_IN",
+            "item_id": item.id,
+            "quantity": 5
+        }
+
+        # First sync
+        response1 = test_client.post("/api/bulk-sync", json={"operations": [operation]})
+        assert response1.status_code == status.HTTP_200_OK
+
+        # Count logs
+        logs_before = test_db.query(AuditLog).filter_by(item_id=item.id).count()
+
+        # Second sync (same UUID)
+        response2 = test_client.post("/api/bulk-sync", json={"operations": [operation]})
+        assert response2.status_code == status.HTTP_200_OK
+
+        # Logs count should be same (no duplicate)
+        logs_after = test_db.query(AuditLog).filter_by(item_id=item.id).count()
+        assert logs_before == logs_after
+
+    def test_sync_preserves_audit_trail(self, test_client, test_db):
+        """Test that audit logs are preserved during sync."""
+        from backend.models import Item
+
+        item = Item(
+            name="Test Item",
+            category="Electronics",
+            item_type="Component",
+            quantity=10,
+            barcode="123456789",
+            part_number="PN-12345"
+        )
+        test_db.add(item)
+        test_db.commit()
+
+        # Perform multiple operations
+        operations = [
+            {"id": str(uuid4()), "type": "CHECK_IN", "item_id": item.id, "quantity": 5},
+            {"id": str(uuid4()), "type": "CHECK_IN", "item_id": item.id, "quantity": 3},
+            {"id": str(uuid4()), "type": "CHECK_OUT", "item_id": item.id, "quantity": 2}
+        ]
+
+        response = test_client.post("/api/bulk-sync", json={"operations": operations})
+        assert response.status_code == status.HTTP_200_OK
+
+        # Verify audit logs
+        response = test_client.get(f"/api/audit-logs?item_id={item.id}")
+        logs = response.json()
+        assert len(logs) == 3
+        assert logs[0]["operation"] == "CHECK_IN"
+        assert logs[0]["quantity_change"] == 5