The aim of this study was to investigate chitosan/DNA complexes formulated with various chitosan salts (CS) including chitosan hydrochloride (CHy), chitosan lactate (CLa), chitosan acetate (CAc), chitosan aspartate (CAs) and chitosan glutamate (CGl). They were assesed for their DNA complexing ability, transfection efficiency in CHO-K1 (Chinese hamster ovary) cells and their effect on cell viability. CHy, CLa, CAc, CAs and CGl, MW 45kDa formed a complex with pcDNA3-CMV-Luc at various N/P ratios. CGl/DNA complexes were formulated with various chitosan molecular weights (20, 45, 200 and 460kDa). The CS/DNA complexes were characterized by agarose gel electrophoresis and investigated for their transfection efficiency in CHO-K1 cells. The cytotoxicity of the complexes was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay in CHO-K1 cells. Gel electrophoresis illustrated that complete complexes formed at N/P ratios above 2 in all CS of MW 45kDa. The transfection efficiency of CS/DNA complexes was dependent on the salt form and MW of chitosan, and the N/P ratio of CS/DNA complexes. Of different CS, the maximum transfection efficiency was found in different N/P ratios. CHy/DNA, CLa/DNA, CAc/DNA, CAs/DNA and CGl/DNA complexes showed maximum transfection efficiencies at N/P ratios of 12, 12, 8, 6 and 6, respectively. Cytotoxicity results showed that all CS/DNA complexes had low cytotoxicity. This study suggests CS have the potential to be used as safe gene delivery vectors.