A chitosanase-producing bacterium, Bacillus cereus D-11, was isolated from an environmental soil sample. The optimal culture condition for chitosanase production by B. cereus D-11 was 3 days of cultivation at 30 o C in a medium composed of 0.5% inoculation concentration (1.4×10 8 CFU/mL), 0.7% colloidal chitosan, 1% yeast extract and 1% NaCl at initial pH 7.0. The highest activity achieved was 7.8 U/mL. The crude enzyme preparation from Bacillus cereus D-11 degraded the chitooligomers pentamer, hexamer, and heptamer into (GlcN)2-4, but not degraded the chitooligomers less than (GlcN)4. These results indicate that B. cereus D-11 chitosanase cleaves the oligomeric chains in the endo-splitting manner and the catalytic domain of D-11 chitosanase recognizes and needs at least 5 glucosamine units for hydrolytic catalysis of the glycosidic linkages.