Objective: To further illuminate a possibme mechanism of Fas/FasL in the treatment of psoriasis, the expression of it and apoptosis of KC were investigated. Methods: With cell culture,immunocytochemistry, the expression of Fas/FasL protein after the treatment with etretin was observed in cultured human normal keratinocytes. Then, the state of apoptosis in cultured keratinocyte after stimuwasn't involved in apoptosis in cultured normol human keratinocytes. But during limited period, the apoptosis of KC could be induced by etretin, thus it can antagonize benign proliferate of keratinocytes. Our data showed up-regulation of the expression of Fas/FasL and apoptosis in cultured human keratinocytes stimulated by etretin, and its function may be involved in the therapeutic machanism of psoriasis.