Abstract: OBJECTIVE To investigate the effect of S-adenosylmethionine(SAMe) on contraction of uterine smooth muscle, and to provide a theoretical basis for novel drug for preterm labor with good characters in safety and effectiveness. METHODS The uterus was dissected from mice at the different time-points: non-pregnant, and earlypregnancy (6.5 d), mid pregnancy (12.5-13.5 d) and late pregnancy (16.5-17.5 d) and the uterus was divided into about 1 cm length in the direction of the longitudinal muscle fibers in the Lock's solution. The muscle strips were fixed to the transducers at both ends. Sulbactamol, SAMe, methionine and taurine were administered by the cumulative concentration administration method, the uterine contraction curves were recorded, measured and analyzed. RESULTS The strong inhibitory effects of salbutamol and SAMe on contraction of isolated uterine smooth muscle of the mice in the early stage (6.5 d), the second trimester (12.5-13.5 d) and the third trimester (16.5-17.5 d) were observed. Salbutamol 10^-7 mol·L^-1 and SAMe 1.0 mmol·L^-1 signifantly inhibited contraction. The effects of the other amino acids (methionine and taurine) on the contraction of isolated uterine smooth muscle in mice were not significant. CONCLUSION SAMe can effectively inhibit the contraction of uterine phases of pregnancy, so SAMe may be a novel relaxation drug for uterine smooth muscle.