Chitosanases (EC 3.2.1.132) are enzymes that catalyze the hydrolysis of chitosan, but not chitin. They are defined as carbohydrolases that hydrolyze partially N-acetylated chitosan, splitting the β-1,4-glycosidic linkages except the N-acetyl-glucosamine homo-linkages (GlcNAc-GlcNAc) [1,E1]. From the view point of sequence and folding similarities chitosanases belong to families 46, 75 or 80 in the classification of glycosyl hydrolases [2,E2]. Chitosanases of families 46 and 80 are enzymes from bacteria and Chlorella viruses that share a conserved active site-related module [3]. This module includes several amino acids essential for enzyme activity and (or) stability as shown by site-directed mutagenesis studies.