Many chitosanases, glycosyl hydrolases that catalyze the degradation of chitosan, have been found in microorganism. In this paper, classification of the enzyme has been described, which is based on the amino acid sequence (families) and splitting patterns (subclasses). Glycohydrolytic mechanisms such as inversion and retention of the substrate anomer are also discussed in context of the families. Interrelationship among the primary structure, clan, anomeric conversion and the splitting patterns has been suggested. In addition, advanced definition of chitosanase was introduced through the investigation of enzymatic products from partially N-acetylated chitosan as a substrate.