The convenient synthesis of core-shell nanoparticles containing degradable components is very desirable given the potential applications of such nanoparticles in biomaterials. A facile approach for producing monodisperse starch-polystyrene nanocomposites with well-defined core-shell structures in the absence of a surfactant was developed. The initially-formed Pickering emulsions underwent conversion into seeded emulsions during the polymerization, wherein the amphiphilic starch-based nanospheres (SNPs) serve as stabilizer and seed. A possible mechanism for this transition was explored based on the morphology and size variations of the emulsion droplets and the resultant nanospheres. The effects of the monomer concentration, SNP content and size, and pH on the core-shell nanospheres were investigated. With increasing monomer concentration, the core size of the particles remained almost unchanged, while the shell layer thickness increased almost linearly. The size of the core-shell nanospheres can be regulated by adjusting the pH and the SNP content and size. (C) 2016 Elsevier Ltd. All rights reserved.