Abstract: The tribological properties of (Ca, Mg) Sialon in dry air and distilled water were examined using an SRV ball on disk test rig. The tribological test results demonstrate that water lubrication reduces the friction coefficients of (Ca, Mg) Sialon but increases the wear volumes as compared with dry sliding, which is attributed to the different wear mechanisms. EPMA,SEM, EDAX and XPS have been utilized to explore the wear mechanisms. Analyses of both worn surface and wear debris indicate that under dry sliding, the major wear mechanisms of (Ca, Mg) Sialon are brittle fracture and abrasion; whereas under water lubricated condition, the main wear mechanism of (Ca, Mg) Sialon is tribochemical wear.