This paper presents a dual band single feed circularly polarized square microstrip patch antenna (SMPA) for WLAN (2.4-2.48 GHz) and WiMAX (5.25-5.85 GHz) wireless communication applications. A square and L-shaped slot is etched inside the radiating patch to achieve dual-band and circular polarization respectively. The electrical size of proposed microstrip patch antenna is 0.22λ × 0.22λ. The antenna is fabricated using FR4 substrate with size of 40 × 40 mm 2 . The antenna resonates at 2.45 GHz and 5.5 GHz with bandwidth of 66 MHz and 121 MHz respectively. The proposed antenna has been fabricated, tested and measured results are presented in this paper.