Chitosan-dendrimer hybrids having various functional groups such as carboxyl, ester, and poly(ethylene glycol) groups were prepared successfully using dendrimer acetal by reductive N-alkylation. The synthetic procedure could be accomplished by one-step reaction without organic solvent. The degree of substitution of dendrimer was 0.13-0.18 evaluated by (1)H NMR. A perfectly or partially water-soluble chitosan-dendrimer hybrid could be obtained. By standard activated sludge, good biodegradation was observed in these hybrids.