To facilitate the bleaching of the hair before bleaching to enable the hair to be bleached so as to have a prescribed color by one operation at the time of the subsequent bleaching of the hair, and to bleach the hair under a good condition.

This pretreating method for the hair bleaching comprises coating a pretreating agent comprising a reducing agent, an alkali agent and water on the hair, heating and holding the coated hair, and drying the heated and held hair.