Objective To study the effects and possible mechanism of Vitamin K2(Vit K_2)in the treatment of K562 cells.Method The possible mechanism of the apoptosis of K562 cells induced by Vitamin K2(Vit K_2)were investigated with the transmission electron microscope,flow cytometry(FCM),retrotrans criptase polymerase chain reaction(RT-PCR)and chemiluminescence assay.Results Apoptosis peak on FCM and positive AnnexinV-FITC on cell membrane showed that Vit K_2 induced apoptosis of K562 cells and in a dose-and-time-dependent manner;G0/G1 cell arrested;significantly down-regulated the expression of bcl-2 and survivin,but had no effect on the expression of bax;The activities of caspase-3 were significantly increased.Conclusions Vit K_2 induces apoptosis of K562 cells through activating caspase-3 pathways and the apoptosis-related genes bcl-2、survivin might play an important role in this process.