A hair treatment composition comprising a thickener comprising a copolymer obtained from the polymerization of at least one nonionic monomer (a) and at least one cationic monomer (b). [Selection figure] None少なくとも1種の非イオン性モノマー(a)と少なくとも1種のカチオン性モノマー(b)との重合から得られる共重合体を含む増粘剤を含む毛髪処理組成物。【選択図】なし