Abstract: An automobile rear body structure includes a pair of rear side frames extending in directions longitudinally of a vehicle body, a cross member extending transversely between the paired rear side frames and having opposite ends rigidly secured to the rear side frames in a rear wheel zone, a rear floor panel rigidly secured at opposite side edges thereof to the rear side frames, and a fuel tank securely mounted on a lower surface of the rear floor panel. A rear portion of each rear side frame extending rearwardly from a joint between such rear side frame and the cross member has increased rigidity compared with a front portion thereof extending frontwardly from the joint.