A buffering structure for the side gates of a cargo box of a truck is disclosed. The buffering structure includes front and rear side gates pivotally mounted on each side of the cargo box, and a middle column interposed between the front side gate and the rear side gate. Buffer members are interposed between the middle column and the front and rear side gates to resiliently support the front and rear side gates. Since the buffer member for resiliently supporting the front and rear side gates is installed on the middle column of the cargo box, deformation of the side gates is prevented and thus the lifespan of the cargo box is extended. Also, the generation of vibration and noise by friction comfort is reduced to improve driving comfort, as well as the smooth opening and closing of the side gates.