This invention provides a skin-smoothing agent which has an effect of beauty treatment, such as moisturizing and smoothing skin, preventing skin from getting rough and wrinkles and preventing skin from deteriorating its elasticity, and also provides products for smoothing skin, such as cosmetics, food and drink, feed and medicine which contain said skin-smoothing agent. The skin-smoothing agent is characterized by containing whey protein hydrolysate as an effective ingredient. Especially, by using the whey protein hydrolysate characterized by that the molecular weight distribution is under 10kDa, with main peak being 200Da to 3kDa, APL(Average Peptide Length)is 2 to 8, the content of free amino acid is under 20%, and the antigenicity is less than 1/10, 000 of the antigenicity of &bgr； -lactoglobulin, it is possible to provide a skin-smoothing agent which is low allergenic and has less bitterness.
