Particulate characteristics were investigated for AlN synthesized by a thermochemical reaction of aluminium aerosol with ammonia gas. The product powders had a decreasing specific surface area between 15.7 and 36.7 m(2)g(-1), with increasing reaction temperature from 1100-1500 degrees C, and the powders with large surface area were strongly hygroscopic. Although the powders were severely aggregated and had a small amount of unreacted aluminium, light milling and post heat treatment made them ultrafine and completely converted. When sintered with 0.5% yttrium at 1900 degrees C, full densification and high thermal conductivity of about 130 W m(-1)K(-1) were obtained.