Objective To study the effect of genistein (Gen) in combination with 5-fluorouracil (5-FU) on human gastric carcinoma cells in vitro. Methods Human gastric carcinoma cell line SGC-7901 was t reated with Gen and 5-FU alone or in combination for 24 , 48 and 72 hours , respectively. MTT assay was used to investigate the inhibitory effect of Gen and 5-FU on SGC-7901 cells. Transmission electron microscopy was used to observe the ultramicrost ructure changes of cancer cells and the flow cytometry was used to detect the distribution of cell cycle. Results Gen and 5-FU alone or in combination inhibited the proliferation of SGC-7901 cells significantly in both time-dependent and dose-dependent manner. The combination of Gen with 5-FU had synergistic effect on the growth of SGC-7901 cell line when the inhibition ratio was 20 % to 80 %. When SGC-7901 cells exposed to 18. 8μmol/ L Gen , 8. 84μmol/ L 52FU , and 3. 06μmol/ L Gen combined with 7. 96μmol/ L 5-FU for 72 hours , 62. 97 % , 63. 76 % and 67. 46 % SGC-7901 cells were arrested in G2 / M , S and G0 / G1 phrase , respectively. Gen and 5-FU could both induce apoptosis and arrest cell cycle of SGC-7901 cells. Conclusion Combination therapy of Gen with 5-FU may take synergistic inhibitory effect on the proliferation of gastric cancer cells by resting cell cycle and inducing cell apoptosis at a certain range of concent ration.