Chitosanase (EC 3.2.1.132) is a class of enzymes that specially hydrolyze the β-1,4-glycosidic linkage within chitosan. Predominantly sourced from bacteria (e.g., Bacillus, Streptomyces) and fungi, it is also found in cyanobacteria, plants, and viruses. Based on amino acid sequences, chitosanases are classified into six glycoside hydrolase (GH) families: GH5, GH7, GH8, GH46, GH75, and GH80. According to substrate cleavage specificity, they are categorized into classes I–IV or the novel DD-4d/Dd-4d typing system. Typical molecular weights range from 20–70 kDa, with optimal activity at pH 4–8 and temperatures of 40–60°C. Metal ions (e.g., Mn²⁺ as an activator; Ag⁺/Hg²⁺ as inhibitors) significantly modulate enzymatic activity. Hydrolysis mechanisms include endo-type (random cleavage of internal bonds) and exo-type (sequential release of monosaccharides from the non-reducing end), yielding chitooligosaccharides (COSs) and D-glucosamine as primary products. To date, eight crystal structures (mainly GH46 family) have been resolved, revealing two catalytic mechanisms: retaining (GH5/GH7) and inverting (GH8/GH46/GH75/GH80). Enzyme performance can be enhanced through heterologous expression, protein engineering (e.g., thermostability improvement), and immobilization techniques. Chitosanase holds significant value for versatile applications in functional oligosaccharide production, biotechnological tool development, and agricultural biocontrol