In subcritical water, MC nylon decomposed completely into water-soluble oligomers without any gas phase product at 345 °C within 45 min, so the solid phase products existed only in the first 40 min of the hydrolytic reaction. The infrared spectra of unreacted MC nylon and the solid product obtained at 15 min of the degradation were investigated to study the chemical composition of solid hydrolytic product. The unreacted MC nylon gave the spectrum basically the same as typical nylon 6 (Fig. 2(a)). Fig. 2(b) obviously indicated that the solid phase product was the incompletely decomposed MC nylon. However a number of noticeable changes appeared in the intensity and area of some absorption bands.