A rear structure of a gaseous fuel vehicle in this invention includes right and left rear frame members, and a support frame mounted to the right and left rear frame members, on which support frame a gaseous fuel tank is mounted. Each of the right and left rear frame members is constituted by a curved member which includes a curved portion curving upward, and a front linear portion and a rear linear portion which are lower than the highest portion of the curved portion. The support frame is attached to the front linear portions and the rear linear portions. The front linear portions are attached to the rear end of a vehicle frame to provide a low floor in a passenger compartment. A load applied to the rear ends of the right and left rear frame members is dispersed into the right and left rear frame members and the support frame, and transmitted to the vehicle frame.