An extracellular chitosanase (AF CSN) was purified from Aspergillus fumigatus and N terminal amino acids of the enzyme were sequenced. Oligonucleotide primer based on the sequence was used to PCR amplify of the chitosanase cDNA. The cloned full length cDNA (csn), 804 bp in size, encoded a single peptide of 251 amino acids. The blast search results of the cDNA sequence showed that the sequence shared the homology with chitosanase of Fusarium solani in two region, specifically but showed no homology with known bacterial chitosanases. The two region have repeated aspartic acid (DIDCD) and threonin (TWTPT) amino acid residue, respectively. This suggests that the chitosanase might have an evolutional origin distinct from bacterial chitosanase. Southern blot analysis results indicated that csn is present as a single copy in the genome of A. fumigatus. The recombinant protein corresponding to the mature protein was generated in E. coli using a plasmid vector pET28a(+). When csn cDNA corresponding to the mature protein was introduced into E. coli and expressed, approximately 28kDa protein was produced in a large amount after IPTG induction.