The corrosion of β-Si 6− z Al z O z N 8− z s (z=1, 2, and 3) prepared by combustion synthesis (CS) followed by spark plasma sintering (SPS) was investigated in supercritical water at 400°C/30MPa for 100h. The corrosion behavior was studied by means of gravimetry, X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive X-ray spectrometer (EDS). The mass loss and corroded layer decreased with the increasing in z value, and the results of XRD showed the oxide formed on β-SiAlONs (z=1, 2, and 3) is aluminum silicate (Al 2 SiO 5 ). Finally, we proposed the reaction mechanism of these materials in supercritical water.