Abstract: Objective To investigate the effect of the sulfated derivatives polysaccharides from sclerotium of Poria cocos(S-PCS3-II)on gastric adenocarcinoma MKN-45 cells apoptosis.Methods The MKN-45 cell line was cultured in vitro,and was exposed to a range of concentrations of S-PCS3-II at different time.The effect of apoptosis was observed by cell morphology,flow cytometry,agarose gel DNA electrophoresis,fluorescent microscopy and transmission electronmicroscopy.Results S-PCS3-II can inhibit the growth of human gastric cancer MKN-45 cells.When MKN-45 cells were treated for 24h,48h,72h at 0.5g/L concentration,the apoptosis rate revealed(7.92±0.83)%、(20.68±1.75)%、(37.52±2.47)%,respectively.DNA agarose gel electrophoresis showed the typical DNA ladder of apoptosis.A typical apoptosis morphology was also observed by fluorescent microscopy.A typical apoptosis ultrastructure changes was also observed by transmission electronmicroscopy.Conclusion S-PCS3-II can inhibit the growth of human gastric cancer MKN-45cells by inducing gastric cancer cells apoptosis.