We investigate the potential of low molecular water-soluble chitosan (LMWSC), LMWSC-methoxy polyethylene glycol (MPEG) [LCP], and LMWSC-MPEG-cholesterol (LCP-Ch) as a gene carrier. LMWSC with free-amine group was formed at the low weight ratio, above a 1:2 weight ratio of plasmid DNA:LMWSC. LCP and LCP-Ch achieved complex formation of above 1:8 and 1:24 by reacting with MPEG and cholesterol (Ch) on the amine-group, respectively. Particle sizes at the pH 6.5 and 7.0 were about 100-120 nm and 120-160 nm, respectively. The surface charge of the complex also depended on the pH. At pH 6.5, the surface charge of the complex was higher than that at pH 7.0. The zeta potential of the LCP modified with MPEG or of the LCP-Ch modified with cholesterol has lower positive value than that of LMWSC because of the decrease of the positive charge. The morphologies of the complexes by transmission electron microscope were of spherelike shape with the average diameters of about 100-150 nm. Among the three gene carriers, LCP-Ch/plasmid DNA showed the highest gene expression owing to the hydrophobic interaction between cell surface and cholesterol. No cytotoxicity was observed in the gene carriers investigated in this study at various concentrations. (c) 2006 Wiley Periodicals, Inc.