The invention provides a novel chlorine-free modified polyolefin resin composition with excellent adherence to nonpolar substrates, with excellent solubility into solvent and compatibility with other resins, and with no tack after painting and drying. It relates to a modified polyolefin resin composition obtainable by graft modifying a mixed resin comprising 40 to 99 parts by weight of polyolefin resin (A) and 1 to 60 parts by weight of ethylenic compound-unsaturated carboxylic acid copolymer (B) that contains 0.1 to 50% by weight of unsaturated carboxylic acid derivative, with unsaturated carboxylic acid derivative and/or its anhydride (C), the modified polyolefin resin composition having weight average molecular weight of 20,000 to 150,000 and the grafting weight of (C) being 0.1 to 20% by weight.