Objective To investigate the effect of melatonin (MT) on the proliferation and apoptosis in human pancreatic cancer cell SW1990 in vitro.Methods SW1990 cell line were treated with MT at different concentrations (0.1,0.5,1.0,2.5 and 5.0 mmol/L) and at different time points (24 h,48 h and 72 h).Cell proliferation was evaluated by MTT and apoptosis was determined by AnnexinV/Pl,cell cycle was determined by flow cytometry,and Western Blot was used to detect the expression of Bcl-2 and Bax.Results MT could inhibit the proliferation of SW1990 cell in a time and dose dependent manner.48 h after 0.1～5.0 mmol/L MT treatment,the proliferation inhibitory rate was 7.4%～85.8%,the proportion of SW1990 cell in phase G0/G1 was 72.6%～85.33%.48 h after 1～5.0 mmol/L MT treatment,the apoptosis rate was 21.5% ～41.7%,and the expression of Bcl-2 was down-regulated and the ratio of Bcl-2/Bax decreased.Conclusions MT could inhibit the proliferation of SW1990 pancreatic cancer cells by up-regulating the expression of Bax and down-regulating the expression of Bcl-2,as well as enhancing apoptosis and blocking SW1990 cell in phase G0/G1.