The present invention relates to a hair treatment agent, and a method for perming hair by using the same, wherein the hair treatment agent comprises: 20-25 wt% of 2-mercapto-4-butyrolactone; and 4-6 wt% of cysteine. The hair treatment agent according to the present invention can alter the shape of hair in various forms without causing damage to the hair, and does not cause unpleasant odors during the procedure.COPYRIGHT KIPO 2017본 발명은 2-머캅토-4-부티로락톤 20 ~ 25 중량%; 및 시스테인 4 ~ 6 중량%를 포함하는 모발 처리제 및 이를 이용한 모발의 퍼머 방법에 관한 것이다.