The present paper describes the tooth surface temperature and the power transmission efficiency of plastic sinecurve gears in the running condition.The plastic sine-curve and involute gears were manufactured by injection molding.The running tests for sine-curve and involute Socks Tights gears were performed under no-lubrication and grease-lubrication conditions, and the tooth surface temperature and the power transmission efficiency were measured.Test results show that the sine-curve gears for operating condition had lower tooth surface temperatures and higher power transmission efficiencies than involute gears under no-lubrication conditions, but in Cup the grease-lubrication condition the superiority of sine-curve gears was not observed.