An object of the invention is to provide a protein-adsorbing material having both adsorption capacity and high-speed treatment performance applicable to not only analysis use but also industrial use, in balance, and to provide a method for producing the same. The present invention provides a protein-adsorbing material comprising a polymer base-material, a polymer side-chain immobilized to the surface of the polymer base-material and a functional group having protein adsorption ability and immobilized to the polymer side-chain, in which the mass of the polymer side-chain is 5 to 30% relative to the mass of the polymer base-material.