In order to study the apoptosic effect of genistein on human gastric carcinoma SGC-7901 cells, DAPI dyeing and DNA electrophoresis were used. Western Blot was used to detect the changes of the expression of p53 protein, Caspase-3 after SGC-7901 cells were exposed to genistein. The results showed that genistein induced cell apoptosis. Genistein also decreased the expression of mutant p53, and increased the protein expression of Caspase-3. These indicated that genistein could induce the apoptosis of gastric carcinoma cells. The inhibition of the expression of mutant p53 and enhance of the protein expression of Caspase-3 would be possible mechanism.