Wireless mesh networks (WMNs) are unpredictable by nature in which ensuring any kind of fairness is challenging. Providing equal opportunity for every node accessing channel, avoiding collisions among nodes which compete for radio resources are the main concerns for the design of an efficient medium access control (MAC) protocol in WMNs. This paper presents an Adaptive distributed coordination function (ADCF) MAC protocol for WMNs which divides the contention window into three windows and adjusts the size of backoff windows as time goes by. Furthermore, ADCF makes use of actual situation to improve the fairness and other performances of networks. Simulation results show that ADCF outperforms distributed coordination function (DCF) protocol in terms of fairness, throughput, average delay and drop ratio.