Wireless technologies provide mobile access and enable rapid and cost-effective network deployment. But a wireless link is generally accompanied by high interference, transmission errors and a varying latency. The erratic packet losses usually lead to a curbing of the flow of segments on the TCP connection, and thus limit TCP performance. This paper presents a threshold control mechanism with cross-layer response approach for improving TCP Vegas performance in IEEE 802.11 wireless networks. By making slight modifications to the legacy IEEE 802.11 MAC and TCP, the numerical results reveal that the proposed scheme provides a significant improvement in TCP performance under IEEE 802.11 wireless environments.