A gene encoding chitin deacetylase was cloned by polymerase chain reaction from Aspergillus nidulans. Sequencing result showed 40% homology to the corresponding gene from Colletotrichum lindemuthianum. The complete gene contains an open reading frame of 747 nucleotides encoding a sequence of 249 amino acid residues. The chitin deacetylase gene was subcloned into a pET28a expression vector and expressed in Escherichia coli BL21 and then purified by metal affinity chromatography using a His-bind column. The purified chitin deacetylase demonstrated an activity of 0.77 U ml(-1) for the glycol chitin substrates, and its specific activity was 4.17 U mg(-1) for it. The optimal temperature and pH of the purified enzyme were 50 A degrees C and 8.0, respectively. When glycol chitin was used as the substrate, K (m) was 4.92 mg ml(-1), and K (cat) showed 6.25 s(-1), thus the ratio of K (cat) and K (m) was 1.27 ml s(-1) mg(-1). The activity of chitin deacetylase was affected by a range of metal ions and ethylenediaminetetraacetic acid.