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Chitosan-DNA nanoparticles were prepared using a complex coacervation process. The important parameters for the nanoparticle synthesis were investigated, including the concentrations of DNA, chitosan and sodium sulfate, temperature of the solutions, pH of the buffer, and molecular weights of chitosan and DNA. At an amino group to phosphate group ratio (N/P ratio) between 3 and 8 and a chitosan concentration of 100 μg/ml, the size of particles was optimized to ∼100–250 nm with a narrow distribution, with a composition of 35.6 and 64.4% by weight for DNA and chitosan, respectively. The surface charge of these particles was slightly positive with a zeta potential of +12 to +18 mV at pH lower than 6.0, and became nearly neutral at pH 7.2. The chitosan-DNA nanoparticles could partially protect the encapsulated plasmid DNA from nuclease degradation as shown by electrophoretic mobility analysis. The …