A rear suspension cross member mounting structure includes a rear floor side member with a 4WD rear cross member mounting hole and a 2WD rear cross member mounting hole, and a reinforcement bracket with a slot corresponding to both the 4WD rear cross member mounting hole and the 2WD rear cross member mounting hole. The structure may further include a bolt, passing through the reinforcement bracket and the rear floor side member to attach the rear cross member to the structure. The bolt may pass sequentially through the reinforcement bracket, the rear floor side member, and the rear cross member, and then engage with a nut provided below the rear cross member.