A production process of a resin composition containing 100 parts by weight of a polyester fiber, 1 to 600 parts by weight of a copolymer of ethylene with a glycidyl group-carrying monomer, and 0.3 to 500 parts by weight of an unsaturated carboxylic acid-modified polyolefin resin, the process comprising steps of (1) melt-kneading the copolymer with the modified polyolefin resin, and (2) kneading the resultant melted resin with the polyester fiber at a temperature lower than a melting point of the polyester fiber.