diff --git a/api/db/services/connector_service.py b/api/db/services/connector_service.py
index 660530c82..838246731 100644
--- a/api/db/services/connector_service.py
+++ b/api/db/services/connector_service.py
@@ -194,7 +194,19 @@ class SyncLogsService(CommonService):
                          update_date=timestamp_to_date(current_timestamp())
                          )\
             .where(cls.model.id == id).execute()
-
+        
+    @classmethod
+    def increase_deleted_docs(cls, min_update, max_update, doc_num, err_msg="", error_count=0):
+        cls.model.update(
+                         docs_removed_from_index=cls.model.docs_removed_from_index + doc_num,
+                         total_docs_indexed=cls.model.total_docs_indexed - doc_num,
+                         poll_range_start=fn.COALESCE(fn.LEAST(cls.model.poll_range_start,min_update), min_update),
+                         poll_range_end=fn.COALESCE(fn.GREATEST(cls.model.poll_range_end, max_update), max_update),
+                         error_msg=cls.model.error_msg + err_msg,
+                         error_count=cls.model.error_count + error_count,
+                         update_time=current_timestamp(),
+                         update_date=timestamp_to_date(current_timestamp())
+                         )
     @classmethod
     def duplicate_and_parse(cls, kb, docs, tenant_id, src, auto_parse=True):
         from api.db.services.file_service import FileService
diff --git a/api/db/services/document_service.py b/api/db/services/document_service.py
index 7b7ef53ec..beedc48d8 100644
--- a/api/db/services/document_service.py
+++ b/api/db/services/document_service.py
@@ -750,6 +750,22 @@ class DocumentService(CommonService):
         for row in rows:
             result[row.kb_id] = row.count
         return result
+    
+    @classmethod
+    @DB.connection_context()
+    def list_document_ids_by_src(cls, tenant_id, kb,  src):
+        fields = [cls.model.id]
+        docs = cls.model.select(*fields)\
+            .where(
+            (cls.model.kb_id == kb),
+            (cls.model.source_type == src)
+        )
+
+        res = []
+        for doc in docs:
+            res.append(doc.id)
+
+        return res
 
     @classmethod
     @DB.connection_context()
@@ -1028,3 +1044,4 @@ def doc_upload_and_parse(conversation_id, file_objs, user_id):
             doc_id, kb.id, token_counts[doc_id], chunk_counts[doc_id], 0)
 
     return [d["id"] for d, _ in files]
+
diff --git a/common/settings.py b/common/settings.py
index 81a2c19a4..e5da8cf85 100644
--- a/common/settings.py
+++ b/common/settings.py
@@ -85,6 +85,8 @@ kg_retriever = None
 # user registration switch
 REGISTER_ENABLED = 1
 
+ENABLE_SYNC_DELETED_CHANGE = os.getenv('ENABLE_SYNC_DELETED_CHANGE', False)
+
 
 # sandbox-executor-manager
 SANDBOX_HOST = None
diff --git a/rag/svr/sync_data_source.py b/rag/svr/sync_data_source.py
index a5c4c4cfb..f9a67be4f 100644
--- a/rag/svr/sync_data_source.py
+++ b/rag/svr/sync_data_source.py
@@ -35,6 +35,8 @@ import trio
 
 from api.db.services.connector_service import ConnectorService, SyncLogsService
 from api.db.services.knowledgebase_service import KnowledgebaseService
+from api.db.services.document_service import DocumentService
+from api.db.services.file_service import FileService
 from common import settings
 from common.config_utils import show_configs
 from common.data_source import BlobStorageConnector, NotionConnector, DiscordConnector, GoogleDriveConnector, MoodleConnector, JiraConnector, DropboxConnector, WebDAVConnector
@@ -62,6 +64,13 @@ class SyncBase:
         SyncLogsService.start(task["id"], task["connector_id"])
         try:
             async with task_limiter:
+                synced_doc_ids = set() #synced document ids for this sync task
+                source_type = f"{self.SOURCE_NAME}/{task['connector_id']}"
+                existing_doc_ids = []
+                with trio.fail_after(task["timeout_secs"]):
+                    # get current synced docs from last sync
+                    existing_doc_ids = DocumentService.list_documents_by_source(task["tenant_id"], task["kb_id"], source_type)
+                         
                 with trio.fail_after(task["timeout_secs"]):
                     document_batch_generator = await self._generate(task)
                     doc_num = 0
@@ -112,6 +121,42 @@ class SyncBase:
                             failed_docs += len(docs)
                             continue
 
+                    if settings.ENABLE_SYNC_DELETED_CHANGE:
+                        task_copy = copy.deepcopy(task)
+                        task_copy.pop("poll_range_start", None)
+                        document_batch_generator = await self._generate(task)
+                        for document_batch in document_batch_generator:
+                            if not document_batch:
+                                continue
+                            docs = [
+                                {
+                                    "id": doc.id,
+                                    "connector_id": task["connector_id"],
+                                    "source": self.SOURCE_NAME,
+                                    "semantic_identifier": doc.semantic_identifier,
+                                    "extension": doc.extension,
+                                    "size_bytes": doc.size_bytes,
+                                    "doc_updated_at": doc.doc_updated_at,
+                                    "blob": doc.blob,
+                                }
+                                for doc in document_batch
+                            ]
+
+                            for doc in docs:
+                                synced_doc_ids.add(doc["id"])
+
+                        # delete removed docs
+                        if not existing_doc_ids:
+                            to_delete_ids = []
+                            for doc_id in existing_doc_ids:
+                                if doc_id not in synced_doc_ids:
+                                    to_delete_ids.append(doc_id)
+                            
+                            if to_delete_ids:
+                                FileService.delete_docs(to_delete_ids, task["tenant_id"])
+                                SyncLogsService.increase_deleted_docs(task["id"], len(to_delete_ids))
+                                logging.info(f"Deleted {len(to_delete_ids)} documents from knowledge base {task['kb_id']} for connector {task['connector_id']}")
+
                     prefix = "[Jira] " if self.SOURCE_NAME == FileSource.JIRA else ""
                     if failed_docs > 0:
                         logging.info(f"{prefix}{doc_num} docs synchronized till {next_update} ({failed_docs} skipped)")