The dependence of high temperature oxidation behavior of beta-SIC coatings on their microstructures were investigated. Sample coatings with various surface morphologies and microstructures were synthesized on graphite by chemical vapor deposition, and were exposed to air or methane combustion exhaust gas at a pressure of 100 kPa and temperatures ranging from 1500 to 1700 degrees C. It was found that the formation of cristobalite decreased with decreasing content of [111]-oriented grains at the specimen surfaces both in air and methane combustion exhaust gas. Because the formation of cristobalite is known to reduce the protectability against oxidation of SiC coatings because of the cracking and peeling of the protective oxide overlayer by thermal expansion and the fast transformation of cristobalite during cooling to room temperature, the present result indicates that oxidation protectability increases with decreasing [111]-oriented grains in the SiC coatings.