Objective: To investigate the mechanism of capsaicin in treating active psoriasis vulgaris. Methods: VIP protein in active psoriatic lesions before and 30 days after the treatment of capsaicin ointment was detected by immunohistochemistry. Results:There was positive expression of VIP in all layers of psoriatic lesions epidermis (95.5 ％ ), but after the treatment of capsaicin ointment,there was nearly no expression of VIP protein in epidermis(22.2％ ). Conclusion: Capsaicin inhibits proliferation and induces the differentiation of keratinocytes through down-regulating the expression of VIP in psoriatic epidermis.