An electrical box support is provided for coupling to the side wall of an electrical box to support the electrical box in an opening formed in a hollow core building block. The support has a flange at the front edge and tab at a front edge that clips onto the side wall of the electrical box. A spring member extends from a rear side edge and curls toward the front edge. The spring member has an end that is directed toward the front edge and spaced from the flange a distance to contact the inner surface of the block while the flange contacts the outer surface of the block. The tab at the front edge of the support has a hook for engaging an inner edge of the electrical box to couple the support to the electrical box and to prevent sliding of the support on the electrical box.