Sub-micron and nano-sized beta-SiC powders were sintered with AlN and Y2O3 as sintering additives by spark plasma sintering (SPS). The sintered densities reached > 95% of theoretical with a different molar ratio of AlN to Y2O3 at total amount of 10vol% and temperature of 1900 degrees C for 10min in N-2 atmosphere under a pressure of 30MPa. With increasing amount of the AlN additive, the size of SiC grains decreased and the shape changed from globular to columnar. The fully densified SiC at AIN:Y2O3=95:5mol% had an average grain size of 0.5-1 mu m and 50-100nm in diameter by using sub-micron and nano-sized SiC starting powders, respectively. Flexural strength of the specimen having grain size of 0.5-1 mu m was approximately 1200MPa at room temperature.