Objective：To investigate the inhibitory effects of L-type Ca2+-channel blocker nifedipine and magnesium sulfate on uterine contractility of full term pregnant women and its relation with labour.Methods: Myometrial strips,prepared from biopsies taken at caesarean section from labouring and non-labouring women at full term pregnancy,were mounted in organ chambers for isometric tension recording.Oxytocin(10-9mol/L) was employed to induce stable contraction.The cumulative effects of nifedipine(10-8,10-7,10-6 and 10-5mol/L) and magnesium sulfate (1,2,4,8 and 16 mmol/L) were studied by calculating the frequency,amplitude and AUC of contractions before and after drug applications,and the inhibitory rates were also calculated.Results: Nifedipine exerted a concentration-dependent relaxant effect on human term pregnant myometrial contractions induced by oxytocin.The relaxant effect was greater in the myometrium of non-labouring than that in the labouring group（P<0.05）.Magnesium sulfate also inhibited the contractility in both groups,with no significant difference between the 2 groups（P>0.05）.Conclusion: Decreased inhibition of human uterine contractility by L-type Ca2+-channel blocker nifedipine in term labouring myometrium may reflect sensitivity changes of Ca2+-channel to nifedipine after the onset of labour.The inhibitory effects of Mg2+ are not affected by labour,suggesting that Mg2+ may also exert its effect on contractility through other pathways besides Ca2+-channel.