Abstract: The friction and wear properties of self mated B 4C under dry sliding in air were investigated on a ring on ring friction and wear tester. The worn surface of B 4C was analyzed by means of X ray diffraction so as to determine the phase composition of the worn ceramic surface. As the results, the friction coefficients decrease with increase of the sliding distance and normal load. The lowest friction coefficient is as low as 0.09, while the initial one ranges from 0.3 to 0.4. X ray diffraction analysis of the worn surface indicates that tribochemical reaction between B 4C and O 2 was involved during the friction process, with the generation of B 2O 3. The resultant B 2O 3 experienced chemical reaction with the moisture in the air to form H 3BO 3, which is responsible for the decrease of the friction coefficients and wear rate. The wear mass loss of the ceramic under the test conditions is immeasurable with a profilometer.