Precipitation polymerization of acrylonitrile in aqueous phase was performed in the presence of submicrometer-sized poly(methyl methacrylate) (PMMA) seed particles. The resulting PMMA/polyacrylonitrile (PAN) composite latex particles showed a novel well-defined surface morphology like rambutan. The formation of such surface structure was ascribed to the facts that PAN polymer is crystalline and scarcely swollen by its monomer. The composite particles had a core/shell structure with a PAN shell surrounding a PMMA core. © 2005 Elsevier Ltd. All rights reserved.