Chitosan-degrading activity induced by chitosan was founf in culture filtrate of Aspergillus flavus IAM2044. Aspergillus flavus IAM2044 had a higher level of chitosanolytic activity when chitosan was used as a carbon source, and yeast extract and peptone were supplemented as nitrogen sources. One of the chitosan-degrading enzymes was purified to homogeneity by ammonium sulfate precipitation followed by cation-exchange and gel filtration chromatographies. The enzyme was monomeric, and its molecular mass was 45 kDa. The optimum pH and temperature of the enzyme were 5.0 and $50^{circ}C$, respectively. The activity was stable in the pH range of 3.5 to 7.0 and at a temperature below $50^{circ}C$. Reaction products analyzed by the viscosimetric assay and thin layer chromatography clearly indicated that the enzyme was an exe-type chitosanase, $exo-{eta}-D-glucosaminidase$, that released GlcN from the nonreducing ends of the oligosaccharide chains.