Abstract: A new microstrip antenna with quite wide bandwidths and simple structure is proposed, which can operate in the both bands at 802.11a/b/g of Wireless Local Area Network (WLAN) and Worldwide Interoperability for Microwave Access (WiMax). The antenna consists of a triangle, a rectangle and a circle radiate units, and it is fed by coplanar waveguide (CPW) and tuned by loading perturbation. It was measured that bandwidths are 34% in the band of 802.11b/g (2.4~2.4835GHz), and the band covered from 2.03GHz to 2.87GHz. In the band of WiMax, the measure result showed that that bandwidths, which covered 3.4~3.7GHz, are 37%. The bandwidth, whose return loss is lower than -10dB, covers from 4.91GHz to 6.83GHz in the band of 802.11a (5.15~5.825GHz). The antenna size is 65mm×50mm×2mm, and it is easy to be integrated in microwave system. In the paper, the structure of the antenna, the simulation and measured results were presented, analyzed and discussed in detail.