The target tracking is one of the main issues in wireless sensor networks (WSNs). In the WSNs, the energy consumption is the most important factor for the network lifetime. In this paper, we utilize the advantage of the grid-based sensor networks to prolong the lifetime of the network. Therefore, we propose Grid-based Mobile Target Tracking Mechanism in Wireless Sensor Networks (GMTT). By the simulation results, we validated the proposed mechanism could efficiently reduce the energy consumption for target tracking.