High thermal conductive AlN ceramics doped with Y2O3 were produced by sintering the powders obtained after applying a carbon coating to the surface of AlN powder grains. During sintering at 1800 degrees C for 1 hour, the carbon reacts with the surface of the AlN grains by carbothermal-reduction of Al2O3, and also with the Al2Y4O9 intermediate phase to form AlN, Y2O3 and CO. By adding 0.56 mass% of carbon, almost all the Al2Y4O9 is reacted and the thermal conductivity increases from 184 W/(m . K) to 224 W/(m . K). Further carbon addition decreases the thermal conductivity and also the final sintered density.