Abstract: Objective 　To study the inflence of Trichosanthin ( TCS) on apoptosis in HeLa cells and its relation with bax and bcl-2 gene expression. Methods 　The inhibitory effect of TCS on HeLa cells was measured with MTT. Cell cycle phase was analysed by flow cytometry. The expressions of bax and bcl-2 protein were detected by Western Blot . Results 　Typical changes of apoptosis such as cell volume minishing and cytoplasm condensing were observed and subdiploid peak can be detected, the expression of bcl-2 decreased but the expression of bax increased along with Trichosanthin's concent ration. Conclusion 　 Trichosanthin can inhibit the growth of HeLa cells, and induce apoptosis in HeLa cells, the down-regulation of bcl-2 and up-regulation of bax may be one of the mechanisms of the apoptosis.