The mechanical and thermal properties of SiC-AlN ceramics were examined in terms of the development of the modulated texture. The SiC-AlN solid solution ceramics with the addition of Y2O3 and Al2O3 were prepared by hot-pressing method, which were followed by the subsequent heat treatment to develop the modulated texture in the miscibility gap at the temperatures of 1600°C or 1800°C. It was found that the flexural strength and Weibull modulus of the ceramics (nominal composition: 70mol% SiC/30mol% AlN) increase from 589 to 674MPa and from 7.6 to 10.5 with the phase separation treatment at 1600°C for 8h. Thermal shock resistance is also enhanced by the phase separation. The addition of AlN to SiC causes a decrease in thermal conductivity. The phase separation does not influence the thermal conductivity of the SiC-AlN solid solution ceramics. The mass gain of the SiC-AlN ceramics due to the oxidation under 1400°C in air is lower than that of SiC ceramics.