A hair dye composition including a first part containing an alkaline agent and a second part containing an oxidizing agent, which are mixed together immediately before use, wherein at least one of the first part and the second part contains a diazacycloheptane represented by the following general formula (1) or a salt thereof, and the pH of the mixture is 7.5 to 12; wherein Z represents a hydroxy group, a primary amino group, or a C1 to C4 acyloxy group; R1 and R2 represent H or a C1 to C4 alkyl group which may be branched; and R3 represents H, a C1 to C6 alkyl or C1 to C6 alkoxy group which may be branched, or an aralkyl or aryl group, having a total of 12 or less carbon atoms, which may have been substituted by one or more C1 to C4 alkyl or alkoxy groups.