diff --git a/src/server/domain/types.py b/src/server/domain/types.py
index 8710da1..8683a09 100644
--- a/src/server/domain/types.py
+++ b/src/server/domain/types.py
@@ -164,15 +164,18 @@ class AssetPrice:
 
     def to_dict(self) -> Dict[str, Any]:
         """Convert to dictionary representation."""
+        # Handle both datetime and date objects for timestamp
+        ts = self.timestamp
+        if isinstance(ts, datetime):
+            ts = ts.isoformat()
+        elif hasattr(ts, 'isoformat'):  # date object
+            ts = ts.isoformat()
+
         return {
             "ticker": self.ticker,
             "price": float(self.price) if self.price else None,
             "currency": self.currency,
-            "timestamp": (
-                self.timestamp.isoformat()
-                if isinstance(self.timestamp, datetime)
-                else self.timestamp
-            ),
+            "timestamp": ts,
             "volume": float(self.volume) if self.volume else None,
             "open_price": float(self.open_price) if self.open_price else None,
             "high_price": float(self.high_price) if self.high_price else None,
diff --git a/src/server/infrastructure/cache/redis_cache.py b/src/server/infrastructure/cache/redis_cache.py
index 1e255cc..6f35fd3 100644
--- a/src/server/infrastructure/cache/redis_cache.py
+++ b/src/server/infrastructure/cache/redis_cache.py
@@ -36,12 +36,52 @@ async def get(self, key: str) -> Optional[Any]:
 
     async def set(self, key: str, value: Any, ttl: Optional[int] = None) -> bool:
         try:
-            await self._cache.set(key, value, ttl=ttl or self._ttl_default)
+            # Serialize value for JSON storage (handles datetime objects)
+            serialized = self._serialize_value(value)
+            await self._cache.set(key, serialized, ttl=ttl or self._ttl_default)
             return True
         except Exception as e:
             logger.error(f"❌ Cache set error for {key}: {e}")
             return False
 
+    def _serialize_value(self, value: Any) -> Any:
+        """Serialize value for JSON storage, handling datetime objects."""
+        # Pydantic model: use mode='json' to convert datetime to ISO strings
+        if hasattr(value, 'model_dump'):
+            return value.model_dump(mode='json')
+
+        # Dataclass with to_dict method
+        if hasattr(value, 'to_dict'):
+            result = value.to_dict()
+            # Recursively handle nested datetime objects
+            return self._serialize_dict(result)
+
+        # List of items
+        if isinstance(value, list):
+            return [self._serialize_value(item) for item in value]
+
+        # Dict with potential datetime values
+        if isinstance(value, dict):
+            return self._serialize_dict(value)
+
+        return value
+
+    def _serialize_dict(self, data: dict) -> dict:
+        """Recursively serialize dict values, converting datetime to ISO strings."""
+        from datetime import date, datetime
+
+        result = {}
+        for k, v in data.items():
+            if isinstance(v, (datetime, date)):
+                result[k] = v.isoformat()
+            elif isinstance(v, dict):
+                result[k] = self._serialize_dict(v)
+            elif isinstance(v, list):
+                result[k] = [self._serialize_value(item) for item in v]
+            else:
+                result[k] = v
+        return result
+
     async def delete(self, key: str) -> bool:
         try:
             await self._cache.delete(key)