Abstract: The present invention relates to a use of alpha-(8-quinolinyloxy) mono-substituted phthalocyanine zinc for the treatment of psoriasis. The use is suitable for various type of psoriasis by utilizing photodynamic therapy. The photosensitizer is used to treat psoriasis by utilizing laser wave length of 670 nm, with high light sensitivity, fast photobleaching, short time needed in protection from light, and avoiding potential toxic and side-effect of photochemistry therapy by using ultraviolet irradiation. The preparation used in the use of ?-(8-quinolinyloxy) mono-substituted phthalocyanine zinc for the treatment of psoriasis includes solution, cream, nanomicelle, microsphere etc, and mode of administration can be systemic or topical administration. The practicability of treating psoriasis by photodynamic therapy has been validated on cell and animal model. The use achieves perfect effect.