A multiple frequency band planar antenna formed on one-side surface of a circuit board comprises: a first antenna pattern, a second antenna pattern, a third antenna pattern and a fourth antenna pattern, each antenna pattern further comprising an elongated portion and a conductor portion; wherein the second elongated portion at a point between its two ends is short-circuited to a feeding transmission line formed on another-side surface of the circuit board through a via. Thus, the multiple frequency band planar antenna can operate at three frequency bands with their central frequencies at 2.4 GHz, 3.5 GHz and 5.8 GHz, respectively, suitable for both WIFi LAN and WiMAX MAN applications.