The present invention provides a treatment composition for dyed hair which effectively prevents color fading of the dyed hair, to thereby maintain the color of the dyed hair for prolonged periods. The composition contains the following components (A), (B), and (C): (A) an organic solvent selected from among aromatic alcohols, lower alkylene carbonates, N-alkylpyrrolidones, and formamides； (B) an organic carboxylic acid or a salt thereof； and (C) a lower alcohol, a polyhydric alcohol, or a lower alkyl ether of a polyhydric alcohol； wherein the pH of the composition falls within the range of 1-6 inclusive, and the composition does not contain any dye. In use, the composition is applied to hair dyed with an acid-dye-type hair dye composition； and then the hair is left to stand for 5-30 minutes at 20-60 DEG C, followed by washing.
