High-density SiC-AlN composites were fabricated from powder mixtures (50:50 in mol) in 1900oC-2100oC temperature range by SPS process. SiC(0.3μm or 0.03μm) and AlN(1.1μm) were used as starting materials. The density of composite increased with increasing firing temperature. From the identification of crystal phase and the change of lattice constant, mixed phases of 3C(β-SiC)ss and 2H(α-SiC/AlN)ss were found at 1900oC and 2000oC, and only 2Hss was found at 2100oC. The OM and EPMA observation indicated that SiC-rich regions (size:10-50μm) existed throughout SiC(0.3μm)-AlN composite because of aggregation of SiC powder. In SiC(0.03μm)-AlN composite, on the other hand, SiC-rich regions (size:submicron) and AlN-rich regions (size: approximately 1μm) existed on a microscopic level at 1900oC, whereras, it was confirmed from EPMA and SEM observation that homogeneous 2H(ss) formed with large grain-growth at 2100oC. The microstructure of SiC(0.03μm)-AlN composite at 2000oC was analyzed to investigate more detailed compositional variation of solid solution. SEM-EDS observation indicated that 3C(ss), SiC-rich 2H(ss) and AlN-rich 2H(ss) existed in SiC(0.03μm)-AlN composite at 2000oC.