To provide a hair treatment agent using poly-γ-L-glutamic acid, having a more sufficient treatment effect than the treatment effects of conventional hair treatment agents, and having sustainability.

The hair treatment agent is characterized by comprising the first agent containing poly-γ-L-glutamic acid and/or a salt thereof, and the second agent containing a cationic group-having surfactant which is dissociated in water, and disorderly and sequentially treating hair with the first agent and the second agent.