The present invention relates to a hair dye composition which is provided by mixing a first-part agent containing an alkaline agent and a second-part agent containing an oxidizing agent upon application, comprising, after mixing, components (a) to (c) and an oxidative dye (d) as needed, wherein the pH after mixing is 8 to 12 and the content of component (a) is 0.1 to 20 wt.%:(a) a betaine compound represented by formula (1) and/or an acid-addition salt thereof:wherein R1, R2 and R3 are the same or different from one another and each represents a Cl-3 alkyl group, X represents a C1-3 alkylene group, Y represents CC2-, S03-, OSO3- and OP03- .(b) an oxidizing agent and(c) an ammonia or a salt thereof.The hair dye composition of the present invention suppresses the stripping of ammonia at the time of mixing a first-part agent and a second-part agent, thereby reducing the unpleasant odor of ammonia upon application. Further, the hair dye composition of the present invention suppresses hair damage and deterioration of feeling without a pre-treatment has excellent dying and bleaching effects and uniformly dyes (bleaches) the hair from the root to the tip of the hair regardless of the degree of hair damage.
