PROBLEM TO BE SOLVED: To provide at least one effect of short treatment time, long-term duration of keratin fiber deformation effect, sufficient perm efficiency, less deterioration of keratin fiber, good color retention and odorless.SOLUTION: A method treating keratin fiber and preferably hair comprises: a step of applying a first cosmetic composition comprising at least one kind of reducing agents onto keratin fiber a step of rising the keratin fiber a first drying step of drying the keratin fiber a step of applying a second cosmetic composition comprising at least one kind of oxidizing agents onto the dried keratin fiber and a second drying step of drying the keratin fiber without rinsing the second cosmetic composition off the keratin fiber.