Chitosan has potential as a biocompatible gene carrier. However, its gene transfection efficiency is low because of its slow endosomal escape rate. Histidine has buffering capacity in the pH range of endosomes/lysosomes. The structure of dendron consists of a central core with several chains radiating from it and many histidines could be conjugated on the surface, increasing the efficiency of histidine modification. The purpose of this study is to increase the gene transfection efficiency of chitosan by promoting its endosomal escape property. We developed fourth-generation lysine-histidine (KH) dendrons that can provide 8 histidines in one dendron molecule. Chitosan-dendron (Chi13k-D) was synthesized using 2-iminothiolane to form the linkage; this was confirmed by NMR and the ninhydrin test. The buffering range, as measured by pH titration, was broader in the Chi13k-D group than in chitosan. Enhanced endosomal escape of Chi13k-D/pDNA complexes was confirmed using fluorescence-labeled endosomes and pDNA. The intralysosomal pH of Chi13k-D/pDNA was also higher than that of chitosan/pDNA. The gene transfection efficiency of Chi13k-D/pDNA was higher than that of chitosan/pDNA in HEK293 cells. These results suggest that KH dendron modification could provide high buffering capacity, which would increase the gene transfection efficiency of chitosan. (C) 2011 Elsevier B. V. All rights reserved.