Chitosanase was purified from the crude enzyme preparation of Bacillus subtilis IMR-NK1. The purified chitosanase had an optimal pH of 4.0, an optimal temperature of 45 degreesC for chitosan hydrolysis. The molecular mass estimated by gel filtration was 36 kDa. Chemical modification agents N-bromosuccinimide (0.05 mM) and p-hydroxymercuribenzoic acid (0.5 mM), and heavy metal ion of Hg2+ (0.1 MM) significantly or completely inhibited the activity of the enzyme. The enzyme also showed activity for hydrolysis of glycol chitosan and colloidal chitin. In the hydrolysis of chitosans of varying N-acetyl content, the enzyme degraded 60-94% deacetylated chitosan most effectively. End products of chitosan hydrolysis by the enzyme were chitobiose to chitotetraose and some chitooligosaccharides with a longer chain length. For chitooligosaccharides hydrolysis, the smallest of the substrates was a glucosamine tetramer.