A frequency reconfigurable slot antenna is proposed. By inserting three p-i-n diodes inside a U-shaped short slot and two L-shaped open slots, which are etched in the ground plane, the antenna can achieve four states: 2.3/5.8 GHz in two single band modes; 2.3/4.4GHz and 4.4/5.8GHz in two dual band modes. The antenna has a size of 25 mm × 27 mm (0.31 λ1 × 0.34 λ1, λ1 is the guided wavelength at the first frequency). Simulated results show that the antenna can operate at 2.3/4.4/5.8 GHz frequency bands and can exhibit good impedance matching, stable radiation patterns.