IEEE802.11 access protocol uses CSMA/CA in its Medium Access control layer as the main access function, which carries several deficiencies. In these networks, as the number of active stations increases, delay and throughput degrade severely. As far as throughput and service delay are vital elements in Quality of Service (QoS) determination, such degradation could lead to intolerable situations and reduce the efficiency of WLANs. Networks (WLANs). Studies proved this problem arises due to constant initial backoff windows size ( ), which is an important parameter in determination of network behavior. In this paper, we introduce a new method to tune this parameter adaptively according to changes in channel load. In this method, we do tune this parameter after every transmission using a feedback from transmission channel. Later it will be proven that applying this method in MAC layer enhances network stability; delay trend in all traffic classes exhibits a considerable reduction when compared with simple Enhanced Distributed Coordination Access (EDCA) scenarios. Also throughput exhibits a salient improvement in level. In other word, QoS improves. Especially, with the aid of this method, delay variations in all decrease considerably and more smoothen delay trends are achieved.