Disclosed is an underbody structure for an automobile, which comprises a pair of laterally-spaced floor frames 10 disposed to extend longitudinally in such a manner as to interpose a tunnel region 6 therebetween and joined to a bottom surface of a front floor portion 2. Each of the floor frames 10 has a rear end located in the vicinity of a rear kick-up portion 3 extending upward from a rear end of the front floor portion 2. The rear kick-up portion 3 and each rear end region of the floor frames 10 are connected to one another from the exterior side of the automobile through an end gusset 45 (47, 48). The end gusset 45 (47, 48) may be designed to define a closed section in cooperation with the rear kick-up portion 3, or to extend laterally outward so as to be connected to a front end region of a rear frame 17. The underbody structure of the present invention can prevent or suppress a rearward movement of each rear end of the floor frames during a head-on collision.
