The rapid progress of wireless communication and embedded micro sensing technologies has made wireless sensor networks possible. Target tracking is an important application of wireless sensor networks. Good tracking quality and energy efficiency are the key requirements for any protocol designed for target tracking sensor networks. In this paper, we present a novel protocol, Adaptive Dynamic Cluster-based Tracking (ADCT), for tracking a mobile target. This protocol uses the optimal choice mechanism and dynamic clusterbased approach to achieve a good tracking quality and energy efficiency by optimally choosing the nodes that participate in tracking and minimizing the communication overhead, thus prolongs the lifetime of the whole sensor network. Simulation results show that our protocol can accurately track a target with random moving speeds and cost much less energy than other protocols for target tracking.