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The IEEE 802.11e is a new standard to support QoS in Wireless LAN (WLAN). A concept called transmission opportunity (TXOP) has been proposed in 802.11e to confine the maximum time duration that a station can be allowed to retain the channel after winning a contention or receiving a QoS- poll from the QAP. Multiple frames can be transmitted within one acquired TXOP without any additional contention or QoS- poll as long as the total transmission time does not exceed the TXOP duration. The 802.11e standard provides the capability to adjust the TXOP value, but it does not specify how this can be accomplished. Real-time video applications such as video streaming and video conferencing which present Variable Bit Rate (VBR) characteristics may need the TXOP to be adaptive to their time varying characteristics. In this paper, we propose an adaptive EDCA TXOP method to improve the QoS support for VBR video transmission under EDCA mode over IEEE 802.11e WLAN. This method takes into account the estimated incoming video frame size and the current transmit queue length to tune the EDCA TXOP after winning a contention. Simulations using real MPEG-1 encoded VBR video trace indicate that our proposed method achieves better QoS support for VBR video traffic than the 802.11e default EDCA TXOP.