The use of wireless networks has spread further than simple data transfer to delay sensitive and loss tolerant multimedia applications. The IEEE 802.11 WLAN has become a dominating technology due to its low cost and ease of implementation. This paper presents across-layer mapping algorithm to improve the quality of transmission of H.264 (a recently-developed video coding standard of the ITU-T video coding experts group) video stream over IEEE 802.11e-based wireless networks. The major goals of H.264 standard have focused on improving the rate distortion process and enhanced compression performance. Our proposed cross-layer design involves the mapping of H.264 video slices (packets) to appropriate access categories of IEEE 802.11e according to their significance information. We evaluate the performance of our proposed cross-layer design and the results obtained demonstrate its effectiveness in exploiting characteristics of the MAC and application layers to improve the video transmission quality.