Chitin oligosaccharides of degree of polymerization 2-4 were deacetylated by purified chitin deacetylase isolated from Colletotrichum lindemuthianum to give their corresponding breakdown products after purification by liquid chromatography. Data from FABMS analyses suggested that N,N ,N ,N -tetraacetylchitotetraose and N,N ,N -triacetylchitotriose were converted into fully-deacetylated corresponding chitosan oligomers. Conversely, N,N -diacetylchitobiose [(GlcNAc) 2 ] was deacetylated to give a product which showed an [M + H] + pseudomolecular ion at m/z 383, suggesting that either of the two acetyl groups were removed. Further data from 1 H NMR analyses confirmed that the reaction product was 2-acetamido-4-O-(2-amino-2-deoxy-β-d-glucopyranosyl)-2-deoxy-d-glucose [GlcN-GlcNAc]. The enzymatic method has three advantageous characteristics over chemical methods: (i) it does not cause unexpected degradation of the sugar chain, (ii) it is highly reproducible, and (iii) unique compounds such as GlcN-GlcNAc may be produced.