PROBLEM TO BE SOLVED: To provide a treatment agent for hair deformation capable of suppressing reduction of the efficiency of imparting a hair shape even when the blending amount of a reductant agent having a thiol-group is reduced, and a treatment method for hair deformation using the treatment agent for hair deformation.SOLUTION: There is provided a treatment agent for hair deformation in which water is blended with one or two or more kinds selected from reducing sugars and which has a pH of 10.0 or more. A treatment method for hair deformation includes a hair deformation step in which the treatment agent for hair deformation is applied to hair and followed by heating.
