Aim: To study the anti-tumour effect of Geraniin isolated from Agrimonia pilosa ledeb. Methods: MTT was used to study anti-tumor effect of Geraniin in vitro. Morphological observation of the cells was completed by fluorescence microscope. The effect of Gerannin on cell apoptosis in human gastric carcinoma SGC-7901 cells was studied by flow cytometry. Results: The proliferation of SGC-7901 cells was inhibited after treated with 0.01, 0.1, 1, 10 and 15µg/ml Gerannin for 72h and the IC50 is 11.5µg/mL. After SGC-7901 cells were treated by geraniin for 24h, morphological changes of apoptosis were observed. The apoptotic cells were detected after treating with 0.01, 0.1, 1 and 10µg/ml of Gerannin for 24h. The rate of apoptosis in SGC-7901 cells induced by gerannin was found to be 7, 11.1, 20, and 27.1%, respectively. Conclusion: Gerannin has anti-tumour effect. Its mechanism of anti-tumour could be attributed to its action of initiating the apoptosis of tumor cells.