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Chitosanase plays an important role in the production of chitooligosaccharides (CHOS), which possess various biological activities. Herein, a glycoside hydrolase (GH) family 46 chitosanase-encoding gene, <i>csnB</i>, was cloned from marine bacterium <i>Bacillus</i> sp. BY01 and heterologously expressed in <i>Escherichia coli</i>. The recombinant chitosanase, CsnB, was optimally active at 35 &#176;C and pH 5.0. It was also revealed to be a cold-adapted enzyme, maintaining 39.5% and 40.4% of its maximum activity at 0 and 10 &#176;C, respectively. Meanwhile, CsnB showed wide pH-stability within the range of pH 3.0 to 7.0. Then, an improved reaction condition was built to enhance its thermostability with a final glycerol volume concentration of 20%. Moreover, CsnB was determined to be an endo-type chitosanase, yielding chitosan disaccharides and trisaccharides as the main products. Overall, CsnB provides a new choice for enzymatic CHOS production.