Sliding Door Mounting Reinforcement Structure and Vehicle Body Provided with the Same

An embodiment sliding door mounting reinforcement structure includes a sliding door lower reinforcement configured to be mounted on a side of a vehicle body along a length direction of the vehicle body, the sliding door lower reinforcement including a guide rail mounted therein, the guide rail being configured to guide movement of a sliding door, and a center floor cross unit configured to be mounted in a width direction of the vehicle body, wherein the sliding door lower reinforcement and the center floor cross unit are combined.