AIM To study the effect of arsenic trioxide(As 2O 3) on inhibition of proliferation human melanoma A 375 cells METHODS The cell proliferation inhibition was measured by MTT colorimetric assay; The expressions of nm23 was determined by immunohistochemistry.RESULTS As 2O 3 could result in the concentration dependent inhibition of A 375 cells proliferation. The volume of IC 50 was 13.05 ?mol?L -1 . The expression of nm23 anti transfergene in A 375 cells could be induced by As 2O 3 (2 ?mol?L -1 ). CONCLUSION As 2O 3 can inhibit proliferation and induce anti transfer protein of A 375 cells.