A simple structured left-handed metamaterials composed of single square ring cell is fabricated. Its permittivity and permeability are simultaneously negative in 4.8-5.25 GHz. A 5.0 GHz microstrip antenna is proposed, and we use this single square ring structured left-handed metamaterials (SSR-LHMs) as covering layer. Simulation and experiment results show that compared with conventional microstrip antenna, the performance of the new microstrip antenna with SSR-LHMs has been improved remarkably. The -3 dB beam of E-plane and H-plane can be reduced respectively by 25 and 20, so the directional property of the antenna is enhanced. The gain is improved by 3dB and the -10 dB bandwidth is increased by 600 MHz.