A multiband T-shaped monopole antenna for WLAN/WiMAX applications is presented. The T-shaped monopole is comprised of two horizontal arms of different lengths, which generate two separate resonant modes for 2.5/5.5GHz WLAN/WiMAX bands, and with a shortened parasitic element, which generates a middle resonant mode for 3.5GHz WiMAX band, for seamless wireless network access applications. The proposed antenna has been successfully simulated and implemented. Both results of simulation and measurement show good agreement. For the lower band from 2.3 to 2.7GHz, the gain varies in the range of 2.5-3.3dB, while the radiation efficiency is from 72% to 85% over the band. As for the middle band from 3.3 to 3.7GHz, the gain varies from 1.5 to 2.0dB, and the radiation efficiency is from 62% to 70%. As for the upper band from 5.2 to 5.8GHz, the antenna gain varies from 5.4 to 5.9dB, and the radiation efficiency is from 63% to 66%.