A compact dual band antenna with two U-shaped slots is presented. The an- tenna structure consists of rectangular patch and a ground plane at the same side. By using two U-shaped slots, the dual band characteristics are successfully obtained. Utilizing a CPW (Coplanar Waveguide) feeding line, the overall dimension of the antenna is 34.5 mm × 40 mm, which printed on an FR4 substrate with a dielectric constant of 2.95 and a substrate thickness of 0.8 mm. Simulation and measurement results show that the antenna impedance bandwidth covers the frequency range of 2.15 to 3.72 GHz. With almost omni-directional radiation pattern, the proposed antenna configuration can be applied to WLAN and WiMAX devices.