A triple-band omni-directional antenna which comprises three pairs of dipoles placed back to back and printed on a dielectric substrate is presented. A prototype is constructed and tested. The experimental results show that the 10dB return loss bandwidth (VSWR greater than2.0) in 2.4GHz, 5.2GHz and 5.8GHz reaches as much as 130MHz, 500MHz and 200MHz, respectively. Moreover, the radiation patterns are almost omni-directional in the azimuthal plane. Peak antenna gain is 1.63dBi, 2.36dBi and 1.54dBi, which indicate that the proposed antenna can be used as a triple-band antenna for the WLAN application.