diff --git a/mem0/memory/main.py b/mem0/memory/main.py
index 333d2510f..80a30cd68 100644
--- a/mem0/memory/main.py
+++ b/mem0/memory/main.py
@@ -341,6 +341,11 @@ def _build_session_scope(filters):
     return "&".join(parts)
 
 
+def _entity_collection_name(provider: str, collection_name: str) -> str:
+    separator = "-" if provider == "s3_vectors" else "_"
+    return f"{collection_name}{separator}entities"
+
+
 setup_config()
 logger = logging.getLogger(__name__)
 
@@ -417,7 +422,7 @@ class Memory(MemoryBase):
         """Lazily initialize entity store on first use."""
         if self._entity_store is None:
             entity_config = _safe_deepcopy_config(self.config.vector_store.config)
-            entity_collection = f"{self.collection_name}_entities"
+            entity_collection = _entity_collection_name(self.config.vector_store.provider, self.collection_name)
             # Set collection name on the cloned config
             if hasattr(entity_config, 'collection_name'):
                 entity_config.collection_name = entity_collection
@@ -1889,7 +1894,7 @@ class AsyncMemory(MemoryBase):
         """Lazily initialize entity store on first use."""
         if self._entity_store is None:
             entity_config = _safe_deepcopy_config(self.config.vector_store.config)
-            entity_collection = f"{self.collection_name}_entities"
+            entity_collection = _entity_collection_name(self.config.vector_store.provider, self.collection_name)
             if hasattr(entity_config, 'collection_name'):
                 entity_config.collection_name = entity_collection
             elif isinstance(entity_config, dict):
diff --git a/tests/test_memory.py b/tests/test_memory.py
index ae3f3ae89..371dd71ae 100644
--- a/tests/test_memory.py
+++ b/tests/test_memory.py
@@ -6,6 +6,7 @@ import pytest
 
 from mem0 import Memory
 from mem0.configs.base import MemoryConfig
+from mem0.memory.main import _entity_collection_name
 from mem0.memory.utils import normalize_facts
 
 
@@ -37,6 +38,14 @@ def test_create_memory(memory_client):
     assert result["results"][0]["memory"] == data
 
 
+def test_entity_collection_name_uses_dash_for_s3_vectors():
+    assert _entity_collection_name("s3_vectors", "test-index") == "test-index-entities"
+
+
+def test_entity_collection_name_keeps_underscore_for_other_stores():
+    assert _entity_collection_name("qdrant", "mem0") == "mem0_entities"
+
+
 def test_get_memory(memory_client):
     data = "Name is John Doe."
     memory_client.add([{"role": "user", "content": data}], user_id="test_user")
diff --git a/tests/vector_stores/test_s3_vectors.py b/tests/vector_stores/test_s3_vectors.py
index aaa0e62dc..68b7fa0f6 100644
--- a/tests/vector_stores/test_s3_vectors.py
+++ b/tests/vector_stores/test_s3_vectors.py
@@ -110,6 +110,32 @@ def test_memory_initialization_with_config(mock_boto_client, mock_llm, mock_embe
         pytest.fail("Memory initialization failed")
 
 
+def test_memory_entity_store_uses_s3_valid_index_name(mock_boto_client, mock_llm, mock_embedder):
+    mock_boto_client.get_vector_bucket.return_value = {}
+    mock_boto_client.get_index.return_value = {}
+
+    config = {
+        "vector_store": {
+            "provider": "s3_vectors",
+            "config": {
+                "vector_bucket_name": BUCKET_NAME,
+                "collection_name": INDEX_NAME,
+                "embedding_model_dims": EMBEDDING_DIMS,
+                "distance_metric": "cosine",
+                "region_name": REGION,
+            },
+        }
+    }
+
+    memory = Memory.from_config(config)
+    assert memory.entity_store is not None
+
+    index_names = [call.kwargs["indexName"] for call in mock_boto_client.get_index.call_args_list]
+    assert INDEX_NAME in index_names
+    assert f"{INDEX_NAME}-entities" in index_names
+    assert f"{INDEX_NAME}_entities" not in index_names
+
+
 def test_insert(mock_boto_client):
     """Test inserting vectors."""
     store = S3Vectors(