A modified polyolefin resin comprising a copolymer having a structure that a propylene-based polyolefin segment (a) and a segment (b) containing a lactic acid as a constituent are bonded in a block state and/or a graft state through a vinyl monomer having a hydroxyl group, wherein a number average molecular weight of the propylene-based polyolefin segment (a) is from 1,000 to 100,000, a number average molecular weight of the segment (b) containing lactic acid as a constituent is from 1,000 to 200,000, and a weight composition of the propylene-based polyolefin segment (a) and the segment (b) containing lactic acid as a constituent is from 10/90 to 90/10. The modified polyolefin resin can be used in a resin composition containing an aliphatic polyester resin (A), a polyolefin resin (B) and the modified polyolefin resin (C). The composition can exhibit excellent heat resistance and impact resistance and can be used for molding various parts.