PEI and chitosan are considered to be promising non-viral gene delivery vectors. To improve the transfection efficiency of chitosan, we linked chitosan with polyethylenimine (PEI, Mw = 1.8 kDa) by 1,1'-carbonyldiimidazole to form a complex. The composition, particle size, as well as the zeta potential of this chitosan-linked-PEI (CP) complex were measured. And the DNA binding ability, cytotoxicity, and gene transfection efficiency of CP complex were also investigated in cancer cells. In HepG2, A549 and HeLa cells, CP complex exhibited lower cytotoxicity as compared with PEI25KDa (Mw = 25 kDa), a positive control proved to be an efficient gene transfection polymer. Likewise, it showed good transfection efficiency in these cancer cell lines. Specifically, the long-term transfection efficiency of CP was higher than PEI25KDa as demonstrated by the in vitro cancer cell model. The confocal laser scanning microscopy data showed the time for CP to enter the nucleus was 4 h, which was longer than that of PEI25KDa but shorter than that of chitosan. Furthermore, CP complexes were used as a gene carrier to deliver the CCL22 gene into H22 cells. When these gene-altered cells were inoculated in mice, the tumor growth rate was significantly decreased, indicating the CP copolymer was a promising vector for the therapeutic gene delivery. (C) 2009 Elsevier B.V. All rights reserved.