The Mobile Wireless Sensor Network (MWSN) is a new style WSN with mobile sinks or sensors in the network. MWSN has advantages over static WSN in the aspect of better energy efficiency, improved coverage, and superior channel capacity. However, mobile nodes also bring some security problems. For example, it is difficult to ensure secure communications among the mobile nodes and static nodes. In this paper, the authors design a lightweight mobile re-authentication protocol for mobile nodes.