Abstract: A rear body structure for a motor vehicle having a rear side frame which extends in a longitudinal direction of a vehicle body on each side at its rear portion and is provided with a thin portion which is so formed as to be thin in thickness in a vertical direction, as compared with other portions that are in front of and at the back of the thin portion, and a protruding portion which protrudes sideways and makes a detour around the thin portion, said thin portion disposed directly between and in contact with a floor panel and the protruding portion, with a spring having a sufficient length for rear suspension being disposed under the thin portion of the rear side frame.