Silicon nitride has been considered as candidate tribological material due to their excellent mechanical and thermal properties. This study investigated the effect of graded grain size on the erosion behavior of silicon nitride at room and high temperatures. Erosion tests were carried out with a gas blast-type erosion tester at temperatures up to 800 °C. Weight loss after impact of SiC particles were measured. The erosion rate varied with temperature and microstructure. Different erosion behavior depending on microstructure were discussed based on SEM observation Auger depth profile of worn surfaces.