We report here the modification of multiwalled carbon nanotubes (MWNTs) with a kind of polysaccharide, carboxymethylated chitosan (cmCs), and their potential usage as donor-acceptor nanohybrids. The modified composites (cmCs/ MWNTs) were characterized by high- resolution TEM, FT- IR, TGA and time- resolved spectroscopy. The time- resolved spectroscopic experiments revealed that interfacial electron transfer readily takes place between MWNTs and surface immobilized cmCs chains. The forward electron transfer is fast (< 20 ns) while the backward recombination is slow. The recombination process strongly depends on the chain length of carboxylmethylated chitosan, i.e. a shorter recombination lifetime (similar to 1.1 mu s) for the shorter- chain cmCs coated MWNTs against that of the longer- chain cmCs coated MWNTs (similar to 3.5 mu s). The results demonstrated that the cmCs/ MWNTs composite may be applied as a controllable donor- acceptor nanohybrid.