The part-mounting structure of the present invention includes a part-mounting portion of a sandwich structure constituted by a core layer and plastic skin layers formed on both surfaces of the core layer, and a part-mounting metal member, at least one of the skin layers having a tapered recess having a sloped side wall and a flat bottom wall, the bottom wall being constituted by the skin layers bonded together, the part-mounting metal member having a bottom plate, and a pair of side plates vertically extending from the bottom plate substantially on both sides, at least one of the side plates having a dent tapered complementarily to the tapered recess of the sandwich structure. The part-mounting metal member is mounted to the part-mounting portion of the sandwich structure with a surface of the tapered recess of the sandwich structure and a surface of the tapered dent of the part-mounting metal member bonded together by an adhesive. This structure is suitable for mounting various parts such as engines, suspension beams, upper arms, radius rods, dampers, seat slide rails, etc. to the vehicle body.