Provided is a second agent for a hair treatment agent, which can satisfactorily mix the first agent and the second agent and can enhance the adherence of the resulting agent to the hair. The second agent for a hair treatment agent of the present invention is a multi-agent hair treatment agent comprising at least a first agent that does not contain or contains an oxidative dye and that contains an alkaline agent, and a second agent that contains an oxidizing agent. Is a second agent used in, and contains a tertiary amine type cationic surfactant. 第１剤と第２剤とを良好に混合することができ、かつ得られる混合剤の毛髪への付着性を高めることができる毛髪処理剤用の第２剤を提供する。 本発明の毛髪処理剤用の第２剤は、酸化染料を含まないか又は含み、かつアルカリ剤を含む第１剤と、酸化剤を含む第２剤とを少なくとも備える多剤式の毛髪処理剤に用いられる第２剤であって、３級アミン型カチオン性界面活性剤を含む。
