Herein a special nanoparticle cluster coated with a porous copolymer is designed and prepared. At first, Ag2O nanoparticles (secondary particles) were fabricated in gelatin solution by a facile chemical approach. Then these nanoparticles were entrapped in a copolymerization system containing gelatin, methyl methacrylate (MMA), an initiator, and using water as a solvent. The nanoparticle clusters coated with porous gelatin-g-PMMA copolymer (Ag2O/gelatin-g-PMMA) were prepared by grafting methyl methacrylate onto gelatin, followed by coating solidification. One significant feature for our approach is that every Ag2O aggregated cluster has been coated with porous gelatin-g-PMMA copolymer film in a unique way, and the Ag2O nanoparticle could penetrate and escape from the coating freely in water by ultrasonication. As a result, this study provides a new approach to prepare monodispersed nanoparticles by ordered porous copolymers with controlled releasing. (c) 2009 Elsevier B.V. All rights reserved.