diff --git a/shadowsocks/shell.py b/shadowsocks/shell.py
index c4b7381..d53e461 100644
--- a/shadowsocks/shell.py
+++ b/shadowsocks/shell.py
@@ -237,6 +237,7 @@ def get_config(is_local):
     config['port_password'] = config.get('port_password', None)
     config['timeout'] = int(config.get('timeout', 300))
     config['udp_timeout'] = int(config.get('udp_timeout', config['timeout']))
+    config['udp_cache'] = int(config.get('udp_cache', 64))
     config['fast_open'] = config.get('fast_open', False)
     config['workers'] = config.get('workers', 1)
     config['pid-file'] = config.get('pid-file', '/var/run/shadowsocks.pid')
diff --git a/shadowsocks/udprelay.py b/shadowsocks/udprelay.py
index 4737199..7fb67b1 100644
--- a/shadowsocks/udprelay.py
+++ b/shadowsocks/udprelay.py
@@ -882,6 +882,7 @@ class UDPRelay(object):
         self._method = config['method']
         self._timeout = config['timeout']
         self._is_local = is_local
+        self._udp_cache_size = config['udp_cache']
         self._cache = lru_cache.LRUCache(timeout=config['udp_timeout'],
                                          close_callback=self._close_client)
         self._client_fd_to_server_addr = {}
@@ -1086,7 +1087,7 @@ class UDPRelay(object):
                         (common.to_str(server_addr), server_port,
                             r_addr[0], r_addr[1]))
 
-        self._cache.clear(256)
+        self._cache.clear(self._udp_cache_size)
 
         if self._is_local:
             ref_iv = [encrypt.encrypt_new_iv(self._method)]