Abstract: OBJECTIVE To investigate the inducing differentiation effect of berberine hydrochloride on B16 mouse melanoma cells. METHODS MTT assay was used to evaluate the inhibitory effect of berberine hydrochloride on proliferation of B16 cells. Morphological changes, melanin content, cloning efficiency and tumorigenicty in C57/BL mice were also used to estimate the differentiation inducing activity of berberine hydrochloride in B16 cells. RESULTS Berberine hydrochloride significantly inhibited the proliferation of B16 cells. After treatment with berberine hydrochloride, B16 cells differentiated into mature epithelia-like cells, cloning efficiency of B16 cells decreased, the content of melanineon increased and tumorigenicty in C57 mice decreased. CONCLUSION Berberine hydrochloride can induce differentiation of B16 cells.