Reactive pyrolysis-gas chromatography (Py-GC) in the presence of oxalic acid was applied to the determination of degree of substitution (DS) in N-carboxyethylated chitin derivatives. On the obtained pyrogram, characteristic products, such as methylacrylate, ethylacrylate and acrylic acid originating from the carboxyethyl branches of the chitin derivatives, were clearly observed together with those from the N-acetyl-d-glucosamine units, such as acetonitrile, acetic acid and acetamide. On the basis of relative yields of these characteristic products, the DS values were precisely evaluated. The results by reactive Py-GC also supported the validity of the results obtained by 1 H NMR that the mono-alkylation onto the amino group of the original chitin was favorable for the derivatization of the samples.