Objective To study the relationship between promyelocytic leukemia(PML) protein and apoptosis and their roles in the pathogenesis of psoriasis. Methods Immunohistochemical techniques were employed to study the expression of PML protein in the uninvolved skin, progressive plaque lesions and regressive lesions. Apoptosis was detected with terminal deoxynucleotidyl transferase-mediated dUTP-DIG nick end labeling(TUNEL). Results There was a significantly upregulated expression of PML protein in progressive plaque lesions, compared with that in uninvolved skin adjacent to the lesions and regressive lesions, and there was nearly no expression in normal skin; there was obvious apoptosis of keratinocytes in the epidermis with intensive PML protein staining. Conclusion The increased apoptosis of keratinocytes in the lesions of psoriasis induced by PML protein might be a homeostatic mechanism to the hyperplasia of keratinocytes.