An extracellular chitinase, produced by Aeromonas sp. DYU-Too7, was purified in the following procedures: ammonium sulfate precipitation, ultrafiltration, chromatographic separation of DEAE-sepharose CL-6B and sephacryl S-100HR. The resulting chitinase has a molecular mass of 36 kDa, an optimal reaction pH of 5.0, and an optimal reaction temperature of 70 ℃. It retains almost 100% activity in the pH range of 5.0-8.0. This chitinase has a high thermal tolerance and retained 90% of its activity at 50 ℃ and 75% at 60 ℃. Enzyme activity was inhibited by Ba2+, Hg2+, Mg2+ and Ag+ cations, but was not substantially inhibited by the K+ cation nor the chelating agent EDTA. The Km and Vmax, using colloidal chitin as a substrate, are 6.3 g/L and 18.69 μmol/min/mg-protein, respectively. The 36 kDa chitinase of Aeromonas sp. DYU-Too7 is an exo-type enzyme, because chitobiose was the main hydrolysate in hydrolysis of colloidal chitin.