Abstract: The tribological behaviours between 25% mass fraction of glass fibers reinforced polyamide 66 composite(25%GF/PA66) and Al₂O₃ ceramic were studied under dry sliding and water lubricating friction condition. The microstructure, micrograph and chemical nature change of the worn surface of 25%GF/PA66 samples were examined using laser optical microscopy, scanning electron microscopy, Fourier transfom infrared spectrometer and X-ray photoelectron spectroscope. The results reveal that the friction coefficients under the water lubricated condition are lower than those of under the dry sliding condition, but the wear volume loss under water lubricating is significantly higher than that of under dry sliding for 25%GF/PA66 composite. Under water lubricated condition, continuous mechanical microcut and the increasing of the temperature induce the deformation of 25%GF/PA66 samples and the hydrolization of the amide groups, which leads the breaking of C—C link and high wear volume loss. The thermal softening temperature of 105.9℃ is estimated based on the generally thermal conductivity model of extended surface.