A chitin-chitosan hybrid polysaccharide (2) having a beta(1-->4)-linked alternating structure of an N-acetyl-D-glucosamine (GlcNAc) unit and a D-glucosamine (GlcN) unit was synthesized via chitinase-catalyzed polymerization of an oxazoline derivative of a GlcNbeta(1-->4)GlcNAc monomer (1). Monomer 1 was designed as a transition-state analogue substrate (TSAS) monomer for chitinase catalysis, which belongs to the glycoside hydrolase family 18. Monomer 1 was effectively polymerized by the catalysis of enzymes from Bacillus sp., Serratia marcescens and Streptomyces griseus, under weak alkaline conditions, giving rise to a water-soluble hybrid polysaccharide (2) in good yields. Molecular weights of 2 reached 2,020 with using chitinase from Serratia marcescens, which corresponds to 10-12 saccharide units.