[Objective]This study was designed to determine growth inhibition of diallyl trisulfide(DATS)in human prostate cancer cells by inducing apoptosis and further to investigate the mechanism underlying such effect.[Methods]Growth inhibition by DATS was estimated by the tetrazolium(MTr)assay.Apoptosis induction in DATS-treated cells was assessed by fluorescence microscopy analysis of cells with condensed and segmented nuclei following staining with DAPI and flow cytometric analysis of cells with sub-G1 DNA content following staining with propidium iodide.Protein levels of apoptosis regulating proteins were determined using western blot.The activity of caspase-3 was measured using a colorimetric assay.[Result]DATS showed tumor growth inhibition in a time-and dose-dependent manner,IC_(50) of DATS was 14 μmol/L at 72 h.DATS evoked apoptosis as confirmed by cell morphology and by the analysis of flow cytometry.The expression of Bcl-2 and Bcl-xL,the apoptosis-suppressing proteins,was more down-regulated.The activity of caspase-3 was enhanced by DATS.[Conclusion]DATS inhibits growth of prostate cancer cells by inducing apoptosis in association with down-regulation of Bcl-2 and Bcl-xL and activation of caspase-3.