diff --git a/lambdas/models/document_reference.py b/lambdas/models/document_reference.py
index 902837cc2..ff1b164d2 100644
--- a/lambdas/models/document_reference.py
+++ b/lambdas/models/document_reference.py
@@ -45,7 +45,6 @@ class DocumentReference(BaseModel):
     uploaded: bool
     uploading: bool
     last_updated: int
-    # file_size: int
 
     def get_file_name_path(self):
         return pathlib.Path(self.file_name)
diff --git a/lambdas/services/document_reference_search_service.py b/lambdas/services/document_reference_search_service.py
index 8f1f4c2bd..37361365d 100644
--- a/lambdas/services/document_reference_search_service.py
+++ b/lambdas/services/document_reference_search_service.py
@@ -49,10 +49,21 @@ def get_document_references(self, nhs_number: str):
                         423, LambdaError.UploadInProgressError
                     )
                 results.extend(
-                    document.model_dump(
-                        include={"file_name", "created", "virus_scanner_result", "id"},
-                        by_alias=True,
-                    )
+                    {
+                        **document.model_dump(
+                            include={
+                                "file_name",
+                                "created",
+                                "virus_scanner_result",
+                                "id",
+                            },
+                            by_alias=True,
+                        ),
+                        "fileSize": self.s3_service.get_file_size(
+                            bucket_name=document.get_file_bucket(),
+                            object_key=document.get_file_key(),
+                        ),
+                    }
                     for document in documents
                 )
             return results
diff --git a/lambdas/tests/unit/services/test_document_reference_search_service.py b/lambdas/tests/unit/services/test_document_reference_search_service.py
index c55396133..e64dbf213 100644
--- a/lambdas/tests/unit/services/test_document_reference_search_service.py
+++ b/lambdas/tests/unit/services/test_document_reference_search_service.py
@@ -12,18 +12,22 @@
     DocumentReference.model_validate(MOCK_SEARCH_RESPONSE["Items"][0])
 ]
 
+MOCK_FILE_SIZE = 24000
+
 EXPECTED_RESPONSE = {
     "created": "2024-01-01T12:00:00.000Z",
     "fileName": "document.csv",
     "virusScannerResult": "Clean",
     "ID": "3d8683b9-1665-40d2-8499-6e8302d507ff",
+    "fileSize": MOCK_FILE_SIZE,
 }
 
 
 @pytest.fixture
 def patched_service(mocker, set_env):
     service = DocumentReferenceSearchService()
-    mocker.patch.object(service, "s3_service")
+    mock_s3_service = mocker.patch.object(service, "s3_service")
+    mocker.patch.object(mock_s3_service, "get_file_size", return_value=MOCK_FILE_SIZE)
     mocker.patch.object(service, "dynamo_service")
     mocker.patch.object(service, "fetch_documents_from_table_with_filter")
     mocker.patch.object(service, "is_upload_in_process", return_value=False)
@@ -83,10 +87,10 @@ def test_get_document_references_dynamo_return_successful_response_single_table(
     patched_service, monkeypatch
 ):
     monkeypatch.setenv("DYNAMODB_TABLE_LIST", json.dumps(["test_table"]))
-
     patched_service.fetch_documents_from_table_with_filter.return_value = (
         MOCK_DOCUMENT_REFERENCE
     )
+
     expected_results = [EXPECTED_RESPONSE]
     actual = patched_service.get_document_references("1111111111")