Provided is a prefabricated shelf assembly. The prefabricated shelf assembly enables a shelf to be conveniently and rapidly assembled, enables the assembled shelf to be firmly maintained, and allows an outer wall and a door to be assembled as a user desires, thus realizing a high-quality product, and allows the length of the shelf to be adjusted via an assembly kit or allows a plurality of shelves to be optionally arranged and then be assembled depending on an installation environment, and adopts a coupling method using a fitting protrusion and a fitting hole, so that the shelf may be re-assembled by separating only a support plate even when the assembly has been completed, and thereby the height of a storage part can be easily changed.