Disclosed herein are an oil-extracted product of indigo naturalis, and the preparation process thereof. Also disclosed is that the oil-extracted product of indigo naturalis can be used in the treatment of psoriasis, especially skin psoriasis and nail psoriasis.本發明揭示一種青黛之經油萃取的產物暨其製備方法。本發明亦揭示該青黛之經油萃取的產物可被用來治療乾癬(特別是皮膚乾癬以及指甲乾癬)。