In this paper in order to improve the performance of the IEEE 802.11e WLAN (Wireless Local Area Network), we propose a simple MAC layer access control mechanism SCAS (Self-Conscious Congestion Avoidance Scheme). During the contention period, if the traffic load is high, we adaptively temporary stop some STAs (stations) contending for the channel to reduce the collision rate according to the network conditions. SCAS is on the MAC layer. Hence, it can not only be applied to the IEEE 802.11e medium access method (EDCA [2]) but also be applied to AEDCF [12]. Besides, each STA can operate SCAS by itself not through AP (Access Point) or higher layer. Finally we evaluate the performance of SCAS on EDCA and AEDCF through simulations. Results show that SCAS can not only reduce collision rate of EDCA and AEDCF efficiently but also improve mean delay time and system throughput especially in high traffic load conditions.