Regioselective introduction of N-acetyl-D-glucosamine and D-glucosamine branches at C-6 of chitin and chitosan has been accomplished. N-Phthaloylchitosan was used;as an organosoluble key intermediate for a series of controlled modification reactions, and the derived 3-O-acetyl-2-N-phthaloylchitosan and 3-O-acetyl-2-N-phthaloyl-6-O-trimethylsilylchitosan proved to be suitable accepters for glycosylation with an oxazoline from glucosamine. The resulting branched product had a substitution degree up to 0.63. It was deprotected to give branched chitosan, which was subsequently N-acetylated to afford branched chitin. The introduction of such branches markedly improved the affinity for solvents, and the product with protecting groups was soluble in common organic solvents in sharp contrast to the insoluble chitin and chitosan. Furthermore, both the branched chitin and chitosan were readily soluble in neutral water and showed high moisture absorption and retention. The branched chitin was degraded with lysozyme, and the susceptibility decreased with increasing extent of branching. The branched chitosan was characterized by marked antimicrobial activity and aggregation ability for bovine serum albumin.