PURPOSE: To improve strength and high-temperature heat resistance without adding a sintering auxiliary by sintering AlN powder having specific particle diameter and oxygen content in a nonoxidizing atmosphere.

CONSTITUTION: AlN powder having ≤1μ particle diameter and ≥0.7wt.% oxygen content is blended with a binder and granulated to give granulated powder, which is molded. The molded article is burnt in a nonoxidizing atmosphere at 1,700-2,200°C to give a sintered material of AlN comprising AlN and a pseudo-polymorphic material of aluminum oxygen nitride, wherein the pseudo- polymorphic material of aluminum oxygen nitride exists in AlN granules and/or independently of AlN granules.