To investigate the effect of VK₃ on arsenic trioxide induced apoptosis of multiple myeloma RPMI8226 ce11s and the molecular mechanisms.Methods:Growth inhibition of RPMI8226 cells exposed to Vitamin K3 Combination with As₂O₃ was analyzed by MTT assay，Annexin V labeling.Results:As₂O₃ alone could inhibit the growth and induce apoptosis of RPMI 8226 cells，whil e As₂O₃ inhibited the proliferation of RPMI8226 cells in a time and dose-dependent manner.Compared with As₂O₃ treatment alone，growth inhibition was enhanced by combination therapy with As₂O₃ and VK₃ (P<0.05)，Annexin V staining showed the earlier apoptotie cells.Flow cytometry showed that the proportion of G₀/G₁ cells was increased and cell proportion in phase was decreased with appearance of apoptosis peak.Conclusion:VK₃ enhances the apoptosis induced by arsenic trioxide in RPMI8226 cells.