Alkaliphilic Bacillus sp. strain J813 produces a novel chitinase (chitinase J). The gene encoding chitinase J (chij) was cloned and sequenced. Deduced amino acid sequence revealed that Chij contained a family 18 catalytic domain, a fibronectin type III-like domain and a chitin-binding domain. Analysis of deletion derivatives indicated that the chitin-binding domain was important for binding to chitin and it enhanced the hydrolysis of insoluble chitin. The subsites existing in the catalytic domain of Chij was thought to bind to insoluble chitosan, although Chij did not hydrolyze chitosan. Some amino acid-substituted mutants were prepared and characterized, suggesting that Glu198 should be the catalytic residue of Chij.