A novel tri-band PIFA antenna operating at WLAN frequency is proposed. The antenna has a two-layer structure, resembling a capital E. By folding the E-shaped structure down, It can largely reduce the size of the antenna. The antenna is feed by the probe, which extends from the ground plane to connect to the radiating strip. The short-circuit strip connects with the ground plane is realized by the probe or shorting wall. The whole structure is the three-dimension version of the simple inverted-F antenna. Three electric current path consititute three resonant mode, corresponding to 2.4/5.2/5.8 GHz, respectively.