diff --git a/python/sglang/srt/arg_groups/serving_hook.py b/python/sglang/srt/arg_groups/serving_hook.py
index 5c3e3f307..e6a7fa496 100644
--- a/python/sglang/srt/arg_groups/serving_hook.py
+++ b/python/sglang/srt/arg_groups/serving_hook.py
@@ -80,6 +80,11 @@ def handle_ssl_validation(server_args: Any):
             raise ValueError(
                 "--http2-max-concurrent-streams must be between 1 and " "4294967295."
             )
+        if not 1024 <= cfg.http2_initial_connection_window_size < 2**31:
+            raise ValueError(
+                "--http2-initial-connection-window-size must be between "
+                "1024 and 2147483647."
+            )
 
         try:
             import granian  # noqa: F401
diff --git a/python/sglang/srt/entrypoints/http_server.py b/python/sglang/srt/entrypoints/http_server.py
index 560a7e44e..2d5c6ffbb 100644
--- a/python/sglang/srt/entrypoints/http_server.py
+++ b/python/sglang/srt/entrypoints/http_server.py
@@ -2445,6 +2445,7 @@ def _run_granian_server(
     port,
     log_level,
     http2_max_concurrent_streams,
+    http2_initial_connection_window_size,
     tokenizer_worker_num=1,
     ssl_certfile=None,
     ssl_keyfile=None,
@@ -2482,7 +2483,8 @@ def _run_granian_server(
         interface=Interfaces.ASGI,
         http=HTTPModes.auto,
         http2_settings=HTTP2Settings(
-            max_concurrent_streams=http2_max_concurrent_streams
+            initial_connection_window_size=http2_initial_connection_window_size,
+            max_concurrent_streams=http2_max_concurrent_streams,
         ),
         log_level=log_level,
         ssl_cert=ssl_certfile,
@@ -2617,6 +2619,9 @@ def _setup_and_run_http_server(
                     http2_max_concurrent_streams=(
                         server_args.http2_max_concurrent_streams
                     ),
+                    http2_initial_connection_window_size=(
+                        server_args.http2_initial_connection_window_size
+                    ),
                     ssl_certfile=server_args.ssl_certfile,
                     ssl_keyfile=server_args.ssl_keyfile,
                     ssl_ca_certs=server_args.ssl_ca_certs,
@@ -2707,6 +2712,9 @@ def _setup_and_run_http_server(
                     http2_max_concurrent_streams=(
                         server_args.http2_max_concurrent_streams
                     ),
+                    http2_initial_connection_window_size=(
+                        server_args.http2_initial_connection_window_size
+                    ),
                     tokenizer_worker_num=server_args.tokenizer_worker_num,
                     ssl_certfile=server_args.ssl_certfile,
                     ssl_keyfile=server_args.ssl_keyfile,
diff --git a/python/sglang/srt/server_args.py b/python/sglang/srt/server_args.py
index 5739ca8a8..90af66ca6 100644
--- a/python/sglang/srt/server_args.py
+++ b/python/sglang/srt/server_args.py
@@ -1283,6 +1283,14 @@ class ServerArgs:
         "connection (1 to 2^32 - 1). Only applies with --enable-http2.",
         NS("serving"),
     ] = 200
+    http2_initial_connection_window_size: A[
+        int,
+        "Initial connection-level HTTP/2 receive window in bytes (1024 to "
+        "2^31 - 1). Only applies with --enable-http2.",
+        NS("serving"),
+    ] = (
+        1024 * 1024
+    )
 
     # -------------------------------------------------------------------------
     # SSL/TLS
diff --git a/test/registered/unit/entrypoints/test_http2_server_config.py b/test/registered/unit/entrypoints/test_http2_server_config.py
index b3881a686..a8be40f83 100644
--- a/test/registered/unit/entrypoints/test_http2_server_config.py
+++ b/test/registered/unit/entrypoints/test_http2_server_config.py
@@ -31,9 +31,14 @@ class TestGranianHTTP2Config(unittest.TestCase):
                 port=30000,
                 log_level="info",
                 http2_max_concurrent_streams=37,
+                http2_initial_connection_window_size=8 * 1024 * 1024,
             )
 
         self.assertEqual(configured["http2_settings"].max_concurrent_streams, 37)
+        self.assertEqual(
+            configured["http2_settings"].initial_connection_window_size,
+            8 * 1024 * 1024,
+        )
 
 
 if __name__ == "__main__":