The pressureless-sintering behavior of AIN-SiC ceramics with 2mass% Y₂O₃ as a sintering aid was investigated. The AIN-SiC composites containing up to 30vol% SiC (two kinds of SiC sources: equiaxed α-SiC and rod-shaped β-SiC particles) were sintered to about 97% of the theoretical density at 2073K in Ar atmosphere of 0.1MPa, and fully densified further by cladless post-HIP-sintering. The mechanical properties including Young's modulus, bending strength and fracture toughness were evaluated for the densely HIPed materials. The Young's modulus was measured from room temperature to 1723K, and the AIN and AIN-SiC composites showed no decrease in Young's modulus at temperatures up to 1473K. The AIN-SiC composites showed increasing bending strength with increasing SiC content, and the highest bending strength was obtained in the AIN-30%SiC composite with rod-shaped β-SiC particles. The fracture toughness of the AIN increased about 60% after the post-HIP treatment due to the toughening effect of elongated grains which was found to be preferably formed in the AIN and AIN-rich composites. The AIN-SiC composites showed no remarkable increase in the fracture toughness with increasing SiC additions, as a result of the decrease in the amount of the elongated grains.