PURPOSE: To provide an acidic hair-treating agent composition containing a kind of anionic surfactant, a specific phosphoric ester surfactant, and a specific hydroxysulfobetaine or amidobetaine, having a pH controlled in an acidic range, and having a conditioning effect and an itch-stopping effect.

CONSTITUTION: An acidic hair-treating agent composition comprises a phosphoric ester surfactant of formula I or II (R1 to R3 are 8-18C saturated or unsaturated hydrocarbon; X, Y are H, alkali metal, ammonium, alkanolamine having a 2-6C hydroxyalkyl group; 1 to n are 0-10), a hydroxysulfobetaine of formula III (R4 is 8-18C saturated or unsaturated hydrocarbon; R5, R6 are lower alkyl), an amidobetaine of formula IV (R7 is 8-18C saturated or unsaturated hydrocarbon; R8 is lower alkylene), and an acidifying agent, and having an adjusted pH of 3-5. The composition has a conditioning effect giving a soft touch to hairs, and can reduce or prevent the damages of the scalps.