It is well known that solid solution is formed in the SiC-AlN system over a wide compositional range. However, the proposed composition range for homogeneous alloy formation is hardly obtained by conventional sintering of powder mixtures of SiC and AlN due to the low diffusivity in the two covalently-bonded compounds. The present study was focused on the preparation of SiC-AlN solid solutions by in-situ HIP-sintering of premixed powder of Si, C and AlN, which was considered to be a handy and less-complicated process as compared to existing ones. It was found that the formation of SiC from Si and C occurred remarkably above the melting point of Si, and fully dense SiC-AlN ceramics could be obtained under the HIP-sintering condition of 2123K and 200MPa. The HIP-sintered compacts showed fine-grained microstructures consisting of SiC-rich and AlN-rich solid solutions with approximate compositions shown in the phase diagram. The mechanical properties, in particular, the fracture strength and hardness of the HIP-sintered SiC-AlN solid solutions and/or mixed composites were better than those of the monolithic SiC and AlN.