Objective: To study the affection of Diallyl trisulfide on cultured human colon carcinoma cell line HT-29 and its mechanism. Methods: The viability of cells after various treatments were determined using the method of MTT. Flow cytometry were used to analyze the change of cell cycle and Bcl-2, Bax levels. Results: The proliferation of human colon carcinoma HT-29 cells were inhibited by Diallyl trisulfide. The inhibition was associated with dose and time dependence. Flow cytometry results showed that: 1) When cells were treated with Diallyl trisulfide at the concentration of 10 ?g/mL for 12 h and 24 h, the percentage of G0/G1 phase cells was decreased and that of G2/M phase cells was significantly increased compared with those in the control group.2) Diallyl trisulfide down regulated Bcl expression, while up-regulated bax expression. Conclusions: It was suggested that Diallyl trisulfide inhibited HT29 cell proliferation. And these were associated with arrest of cell cycles and down regulation of Bcl2/Bax ratio.