Abstract: An underframe structure for a motor vehicle, the underframe structure comprising a floor (12), and at least two longitudinal side members (14) respectively disposed on each side of the floor (12); the floor (12) is divided into at least one front unit (16) and one rear unit (18) fixed to a transverse heel board (24). The underframe structure also comprises a lateral reinforcement part (26) which comprises at least one elongate body extending from the heel board towards the closest side member, the lateral reinforcement part is fixed on one side to the heel board (24), and on the other side to the front unit (16) of the floor (12) or to a side member (14) in the region of the front unit (16) of the floor.