A method for conducting hair dying and curly hair straightening continuously, said method being characterized by comprising the steps of: subjecting hair to a dying treatment; applying a reducing first preparation containing a basic dye and/or an HC dye onto the hair immediately after the dying treatment and then allowing the hair to leave for a predetermined time to achieve a reduction treatment of a cystine bond; straightening the reduced hair; applying an oxidizing second preparation onto the straightened hair and then allowing the hair to leave for a predetermined time to achieve an oxidization treatment for regenerating the cystine bond.