Abstract: An Unattended Wireless Sensor Network (UWSN) collects the sensing data by using mobile sinks (MSs). It differs from the traditional multi- hop wireless sensor networks in which unbalanced traffic makes the sensors close to the base station deplete their power earlier than others. An UWSN can save the battery power and prolong the network lifetime. Unfortunately, MSs would be given too much privilege when acting as the collecting base station, which will cause security concern if Replicated. Besides, UWSNs are usually deployed in unreachable and hostile environments, where sensors can be easily Replicated. Thus, their security issues should be carefully addressed to deal with node compromise. In this paper, we present a novel key management scheme to secure UWSNs. We employ the Blundo symmetric polynomial mechanism to guard against the newly Replicated nodes in a period while utilizing the periodic key updating based on the reverse hash chain to block the Replicated nodes and revoke the Replicated MSs if failing the authentication. We show that our scheme is robust against node Replicated attacks and carry out comparison analysis on the intrusion-tolerance ratio, communication and computing overhead.