To obtain an oxidative hair dye composition reducing affecting the hair in hair dyeing and improving the gloss and smoothness of the hair without making the hair stiff after dyed, and to provide an oxidative hair dyeing agent using the composition.

The oxidative hair dye composition comprises 0.05-10 wt.% of an amine oxido group-containing resin with a weight-average molecular weight of 5,000-1,000,000 composed of amine oxido group-containing recurring units corresponding to those derived from an amine oxido group-containing ethylenically unsaturated monomer and optionally containing recurring units corresponding to those derived from another ethylenically unsaturated monomer, and at least one oxidative dye.