The core-shell nanoparticles composing of poly(methyl methacrylate) (PMMA) cores surrounded by various acid-modified chitosan shells were synthesized via a surfactant-free emulsion copolymerization induced by tert-butylhydroperoxide (TBHP). Methyl methacrylate (MMA) was grafted onto chitosan, modified with hydrochoric, lactic, aspartic, and glutamic acids. MMA conversions were up to 64 % . The prepared nanoparticles had diameter ranging from100 to 300 nm characterized by atomic force microscopy (AFM) and displayed highly positive surface charges up to +77 mV. Transmission electron microscopic (TEM) images clearly revealed well-defined core-shell morphology of the nanoparticles where PMMA cores are coated with acid-modified chitosan shells. The effects of acid-modified chitosans on particle size, intensity of surface charge, morphology, and thermal stability were determined systematically. The complexed plasmid DNA/nanoparticles were investigated with zeta potential. Results suggested that these nanoparticles could effectively complex with plasmid DNA (pDNA) via electrostatic interaction and could be used as potential gene carriers.