Abstract: In this study, a novel carbohydrate 18 family chitinase gene Machi3 was cloned from the genomic DNA of marine microorganism Micromonospra aurantiaca and successfully expressed in Escherichia coli. The optimal reaction temperature and pH for MaChi3 were 55  ℃ and 7.0, respectively. MaChi3 showed good stability below 55  ℃ and at pH of 6−9. The activity of MaChi3 was slightly promoted by Mg²⁺, Ca²⁺, Tween 40 and Tween 80. The recombinant chitinase showed hydrolytic activity toward α-chitin, colloidal chitin, shrimp shell powder, chitosan (50%−95% of deacetylation), starch and cellulose, among which the highest activity of 2.24 U mg⁻¹ was observed in colloidal chitin. The results of scanning electron microscopy suggests that the fiber structure of chitin became loose after pretreatment with HCl, so it was more favorable to the hydrolysis of MaChi3. The K_m and V_max values of MaChi3 toward colloidal chitin were 5.93 mg·mL⁻¹ and 8.58 μmol·(min·mg)⁻¹, respectively. In addition, the main product of colloidal chitin hydrolyzed by MaChi3 was N, N-diacetyl chitobiose with a yield of 285.54 mg·g⁻¹. MaChi3 shows good catalytic activity, which is beneficial for its development and application in biotransformation of chitin.