Abstract: The present invention has an object to provide damaged hair improving agents and damaged hair improving cosmetics containing the same, capable of providing excellent improving effects on damaged hair without using cumbersome work and an expensive special component and retaining the effects for an extended period of time. It was found that by using one or more selected from specific L-ascorbic acid derivatives and salts thereof, which had been conventionally used in cosmetics as useful components due to physiological activities such as a skin-whitening effect, as hair improving agents, and further containing these in a hair cosmetic and applying the hair cosmetic to damaged hair, improving effects such as increasing the hydrophobicity on the damaged hair surface and further enhancing the smoothness of hair were exhibited. Thus, the damaged hair improving agents and the damaged hair improving cosmetics containing the same effective on damaged hair have been provided.