PURPOSE: To obtain an acidic hair dyeing agent composition by improving its utility giving fluidity while satisfying essential conditions such as dyeing properties and washing resistance as an acidic hair dyeing agent and using the xantham gum having as a thickening agent.

CONSTITUTION: (A) Xanthan gum as a thickening agent is blended with (B) bentonite and/or crosslinkable sodium polyacrylate in the ratio of 0.5-5.0wt.% component A and 0.1-1.0wt.% total amount of the component B and preferably (C) 0.01-5.0wt.% total amount of one or more silicones to give an acidic dyeing agent having excellent dyeing properties, washing resistance and fluidity and in the case of possession of the component C, having smooth touch after use besides these characteristics. The component is applicable to a hair dyeing composition also useful as rinse after shampooing by making the most of characteristics as a one-pack type agent.