A chitinase gene belonging to the glycoside hydrolase family 19 from Vibrio proteolyticus (chi19) was cloned. The recombinant enzyme (Chi19) showed weak activities against polymeric substrates and considerable activities against fully N-acetylated chitooligosaccharides, (GlcNAc)(n), whose degree of polymerization was greater than or equal to five. It hydrolyzed (GlcNAc)(n) at the second linkage position from the reducing ends of the chitooligosaccharides. The hydrolytic products of colloidal chitin were mainly (GlcNAc)(2) from the initial stage of the reaction. The hydrolytic pattern of reduced colloidal chitin clearly suggested that the enzyme hydrolyzed the polymeric substrate from the reducing end.