The apoptosis in gastric cancer cells induced by genistein and the relationship between this apoptosis and expression of NF-κB and Caspase-3 were studied. In vitro experiments, MTT assay was used to determine the cell growth inhibitory rate. Transmission fluorescence microscope, transmission electron microscopy, DNA-fragment assay were used to qualitively detect the apoptosis status of gastric cancer line SGC-7901 before and after the genistein treatment. Immunohistochemical staining and Western Blotting were performed to detect the expression of gene NF-κB and Caspase-3. The results showed that genistein inhibited the growth of gastric carcinoma cell line SGC-7901 in a dose-and time-dependent manner. Genistein induced SGC-7901 cells to undergo apoptosis with typically apoptotic characteristics, including morphological changes of chromatin condensation, chromatin crescent formation, nucleus fragmentation and apoptotic body formation. Genistein could reduce the expression of gene NF-κB, and improve the expression of gene Caspase-3.