Abstract: The human melaonma cell line was used as study for experimental differentiation by retinoic acid （RA）. The results showed: RA had a certain effect of growth inhibition for melanoma; doubling times of the cells was delayed; melanoma cells treated by RA were transplanted into nude mouse subdermatos and the growth of the tumors became slow; the melanoma cells may transform from epithelioid cells into fibroblast-like or dentritic cells. Elcctronmicroscopically, the cells with RA treatment had more organella. Melanosomes could be found in some cells. Immunohistochemically, HLA-DR was positive in control group and negative in RA treatment group. The tyrosinase activity appeared potentially increasing. Oncogene v-src expression decreased. These results suggested that the effects of RA were various ways, including cell surface antigen, oncogene and enzyme activity etc.