A one-step way to prepare organosilica@chitosan crosslinked nanospheres was developed through self-assembly of amphiphilic copolymers synthesized by concurrent grafting polymerization and sol-gel reaction. The core organosilica was formed by hydrolysis and condensation of an alkyloxosilane-3-(trimethoxysilyl) propyl methacrylate (TMSPM) that was simultaneously polymerized using chitosan/tert-butyl hydroperoxide (TBHP) as redox-pair initiator. The well-defined nanospheres had adjustable sizes below 100 urn, and had not harmful residues impeding medical applications. This synthesis method simplified the preparation of silica @polymer spheres by eliminating the previous core-forming step, and could apply many water-soluble biopolymers containing -NH2 groups as the shell materials. (c) 2006 Elsevier Ltd. All rights reserved.