A chitosanase was purified from the culture fluid of the chitino- and chitosanolytic bacterium Burkholderia gladioli strain CHB101. The purified enzyme (chitosanase A) had a molecular mass of 28 kDa, and catalyzed the endo-type cleavage of chitosans having a low degree of acetylation (0–30%). The enzyme hydrolyzed glucosamine oligomers larger than a pentamer, but did not exhibit any activity toward N-acetyl-glucosamine oligomers and colloidal chitin. The gene coding for chitosanase A (csnA) was isolated and its nucleotide sequence determined. B. gladioli csnA has an ORF encoding a polypeptide of 355 amino acid residues. Analysis of the N-terminal amino acid sequence of the purified chitosanase A and comparison with that deduced from the csnA ORF suggests post-translational processing of a putative signal peptide and a possible substrate-binding domain. The deduced amino acid sequence corresponding to the mature protein showed 80% similarity to the sequences reported from Bacillus circulans strain MH-K1 and Bacillus ehimensis strain EAG1, which belong to family 46 glycosyl hydrolases.