Abstract. Providing energy efficiency in MAC (Medium Access Control) layer, while achieving desirable throughput, is an important research issue in the area of wireless networking. A wireless LAN such as IEEE 802.11 using the Distributed Coordination Function (DCF) also provides a mechanism for power conservation which allows each node to “sleep” for some amount of periods, but also requires the nodes to wake up periodically and stay “awake” for a certain duration called the ATIMWindow. In this paper, we propose a new energy-efficient MAC protocol that allows the nodes to go to sleep early, without the need to be “on” for the whole ATIM interval, in the case they are acknowledged that no data is buffered within an ad hoc network and therefore no data transmission will be taken place.