Timing synchronization is essential to wireless sensor networks. TDMA-based MAC protocols depend on the accurate synchronization to conduct transmissions. Synchronized with each other, sensor nodes are able to determine when they should be turned on/off to achieve power management which is especially important in wireless sensor networks. In this paper, we propose a power-efficient timing synchronization protocol (PETSP) which aims to fulfill the synchronization job with the minimum energy consumption. In PETSP, all sensor nodes synchronize their timing to a designated target node. This mechanism speeds up the synchronization process. When the clock oscillation difference to the target node is collected, it is possible for a sensor node to self-correct its timing. This self-correction avoids exchanging synchronization messages all the time. Based on this observation, our PETSP achieves power conservation by enlarging the synchronization period. Simulation results show that our PETSP achieves synchronization fast. It also decreases 47% and 75% the power consumption and average maximum clock drift as compared to the IEEE 802.11, respectively. We have also implemented the proposed timing synchronization mechanism on MICA Mote sensor boards. The experiments verify that the protocol achieve timing synchronization in a real system.