A novel compact triple-frequency wide-slot antenna for WLAN/WiMAX applications is proposed and investigated in this paper. The presented antenna is simply composed of an inverted Ushaped slot, a microstrip feed line, a vertical conducting strip, and a L-shaped stub. By adjusting the dimensions of the feed line, strip and stub, three desired resonant frequencies can be achieved and adjusted independently. Experimental results show that the antenna impedance bandwidths for S 11 ⩽ −10 dB are 2.34–2.55 GHz, 3.23– 3.71 GHz, and 5.13–5.85 GHz, covering the 2.4/5.2/5.8 GHz WLAN bands and 3.5/5.5 GHz WiMAX bands. Furthermore, nearly omnidirectional radiation patterns and appreciable gain over the operating bands have been obtained.