AlN-15BN composite ceramics were produced via pressureless sintering process with BN powders bought from market and AlN powders synthesized by carbothermal reduction method as starting materials, and Y2O3 as sintering aids. The effects of sintering temperature on the phases, density, microstructure of AlN-BN ceramics were studied. The results showed that Y2O3 reacted with Al2O3 presenting on the surfaces of AlN particles and formed liquid phases to promote the densification. The density, thermal conductivity and hardness increased with the increas of sintering temperature, and the plate-like BN crystalline could form a card-house structure which hampers the densification of composite ceramics. AlN-BN composite ceramics with thermal conductivity 104.2 W?m-1?K-1, relative density 86.4% and HRA hardness 562 MPa were produced after being sintering at 1 850 for 3 h.