Scarce resources of wireless medium (e.g., bandwidth, battery power, and so on) significantly restrict the progress of wireless local area networks (WLANs). Heavy traffic load and high station density are most likely to incur collisions, and further consume bandwidth and energy. In this paper, a distributed power-saving protocol, Power-Efficient MAC Protocol (PEM), to avoid collisions and to save energy is proposed. PEM takes advantage of power control technique to reduce the interferences among transmission pairs and increase the spatial reuse of WLANs. Based on the concept of Maximum Independent Set (MIS), a novel heuristic scheme with the aid of interference relationship is proposed to provide as many simultaneous transmission pairs as possible. In PEM, all stations know when to wake up and when they can enter doze state. Thus, stations need not waste power to idle listen and can save much power. The network bandwidth can be efficiently utilized as well. To verify the performance of PEM, a lot of simulations are performed. The experimental results show that with the property of spatial reuse, PEM not only reduces power consumption, but also leads to higher network throughput in comparison with the existing work, such as DCF, DCS, and DPSM.