The well-defined core-shell amphiphilic nanoparticles consisting of the poly(methylmethacrylate) (PMMA) cores surrounded by the modified chitosan shells were prepared via a surfactant free emulsion graft copolymerization of methyl methacrylate from an aqueous modified chitosan solution induced by a small amount of tert-butyl hydroperoxide. Chitosan has been modified to several salt forms such as chitosan hydrochlorate, chitosan aspartate, chitosan glutamate and chitosan lactate. Different types of PMMA-chitosan core-shell particles have an average particle diameter in the range of 300-800 nm depending on modified chitosan shell. Transmission electron microscopic (TEM) images clearly reveal well-defined core-shell morphology of the nanoparticles where the PMMA cores are coated with chitosan shells. The core-shell nanoparticles were investigated as novel carriers for gene delivery.