A rear body structure of a vehicle is provided with a space, defined under a floor panel between a passenger room and a trunk room, in which a fuel tank is received. The structure includes support beams for supporting the fuel tank from an underside, in a fuel tank space. The space is formed by bending up and down a floor panel in a lengthwise direction of the car body, such as the rear floor panel of the passenger room and the trunk floor panel of the trunk room. The support beams include a pair of support beams, disposed in parallel and extending in a lengthwise direction of the car body, and a pair of connecting beams, extending in a transverse direction of the car body between and connected to the supporting beams, which are assembled as parallel crosses.