The corrosion behavior of sialon ceramics was investigated in supercritical water at 450 degrees C under 45 MPa for 2-50 h. alpha-sialon exhibited better corrosion resistance than beta-sialon and alpha/beta-sialon. Pitting corrosion with the formation of corrosion products was observed in the case of beta-sialon and alpha/beta-sialon. By contrast, the corrosion behavior of alpha-sialon was characterized by uniform corrosion with the formation of corrosion products. The degree of strength deterioration was strongly dependent on the corrosion morphology. The bending strength of alpha-sialon after corrosion for 30 h was about 90% of its initial strength, while the strength of beta-sialon decreased to 65% of its original strength.