To adhere an enzyme and a coenzyme to a fiber product and then apply the treated fiber product to clothes, night cloth materials, automotive or vehicle interiors or interior products to impart functions such as skin-beautifying effects, anti-ageing effects (freshness-retaining property, effects for preventing the oxidation of the skins with active oxygen), anti-allergy, anti-atopic dermatitis, and the like.

This fiber-processing agent is characterized by binding an enzyme, especially an enzyme called apoenzyme, to a coenzyme of low mol.wt. compound, or by carrying an additive such as lecithin on a coenzyme. The fiber-processing agent is applied to a fiber product in an form easily exhibiting the original functions and performances of the enzyme and the coenzyme to impart the skin-beautifying effects, anti-ageing effects (freshness-retaining property, effects for preventing the oxidation of the skins with active oxygen), anti-allergy, and anti-atopic dermatitis to the fiber product.