Abstract: A novel polarization reconfigurable microstrip antenna is proposed by using the complementary split ring resonator (CSRR) structure. The CSRR with a PIN diode switch is loaded on the ground plane of the antenna. By controlling the state of the diode switch, the left hand circular polarization and the linear polarization of the antenna can be agile without extra bias circuits being required. Effects of the size and position of the CSRR on the antenna circular polarization characteristic have been analyzed using simulation software. The designed antenna operates on the band of 5. 8GHz and the measured results meet well with the simulation. The measured results show that the circularized polarization operates at 5. 77GHz center frequency with the -10 dB bandwidth of about 360MHz. The 3dB axial ratio bandwidth is 80MHz with the minimum value of 1. 5dB. The linear polarization operates at 5. 72GHz with the -10dB bandwidth about 200MHz. The antenna has about 6dB gain for both polarization and good radiation patterns, which can be applied to modern wireless communication systems.