A novel wide band U-shaped monopole antenna with two C-shaped parasitic elements, suitable for WLAN and WiMAX operations, is pretented experimentally and numerically. The wide-band characteristics are obtained by using the U-shaped patch and the two C-shaped parasitic elements along the CPW signal strip. And the simulated wide antenna yields a 10dB impedance bandwidth range from 2.51GHz to 6.0GHz. The antenna is as small as 20×30×1.6mm3. The investigated antennas have been successfully designed, simulated, showing good impedance bandwidth and omni-directional radiation patterns.