In this paper, a meandered monopole antenna with an extended back ground plane is proposed for WLAN USB dongle application. The meandered monopole excites a resonant mode at 2.4 GHz while the extended ground plane operates a higher mode for 5.15 GHz bands. A U-shaped strip is added to adjust the antenna's matching. From the simulated and measured return loss, the 10 dB operating bands cover the IEEE 802.11 a/b/g WLAN application bands. Although the proposed antenna occupies a small dimension of 37 mm × 6.5 mm, the antenna's performances are suitable for applying in WLAN system.