A novel thermostable extracellular chitinase was purified from the culture filtrate of Thermomyces lanuginosus SY2 by using diethylaminoethyl Sepharose chromatography and Phenyl-Sepharose chromatography. The molecular size of the purified chitinase was estimated to be 48 kDa by sodium dodeeyl sulfate-polyacrylamide gel electrophoresis. The chitinase exhibited optimum catalytic activity at pH 4.5 and 55℃. The enzyme was stable at 50℃, and its half-life time at 65℃ was 25 min. The thermostable chitinase was obtained with 60% of the full activity, when it was incubated in the buffer (pH 2.5). The enzyme showed the unique properties for thermostability and pH stability since it was one of the most thermostable ehitinases so far isolated in fungi. Ca2+, Ba2+, Na2+, and K+ enhanced the enzyme activity, whereas Fe2+, Ag+, Hg2+, and ethylene diamine tetraacetic acid caused obvious inhibition. The N-terminal amino acids were AQGYLSVQYFVNWAI. Degenerate primers based on the N-terminal sequences of purified chitinase and a cDNA fragment encoding the chitinase gene were obtained through reverse transcriptase-polymerase chain reaction amplieation. The RACE was used to generate full-length cDNA clones. The cDNA of chit contained an open reading frame of 1 326 bp encoding 442 amino acids. The gene chit has been registered in GenBank with accession number DQ092332. The alignment results of putative amino acid sequence showed the lower similarity to other chitinases in family-18 except for the catalytic domain containing two conserved motifs related with catalytic activity of chitinase.