A folding box is provided. The folding box includes a bottom plate, a two side plates opposite to each other, a front plate, and a rear plate combined with one another. While in use, the above plates are expanded to form a box for mounting different objects. While not in use, the above plates are folded for storage. During expansion or folding of the folding box, touch fasteners are used to adhere and fix the respective plates tightly. Thereby overall weight of the folding box is lighter and the folding box is capable of being folded for minimizing storage space occupied while not in use. After being folded, the folding box is positioned precisely, unable to be expanded freely. Therefore, the folding box is more convenient to use.