In this paper, for the first time, chemically modified dendrimer-ZnO nanocomposite was prepared and used for the photodegraclation of an azo dye naphthol blue black (NBB) under UV light. Initially, ZnO was prepared by simple physical grinding of zinc acetate with sodium hydroxide under solvent free condition. The chemical modification of ZnO was carried out by binding poly(amido amine) (PAMAM) dendrimer through glycidoxypropyltrimethoxy silane as a binding agent. The formation of rod like dendrimer-ZnO nanocomposite was confirmed by different characterization techniques. The photocatalytic activity was highly influenced by initial pH of dye solutions. This catalyst was reusable. (C) 2014 Elsevier B.V. All rights reserved.