The high thermal conductive aluminum nitride sintered body according to the present invention has: a thermal conductivity of 220 W/mK or more; and a three point bending strength of 250 MPa or more; wherein a ratio (I.sub.Al.sub.2.sub.Y.sub.4.sub.O.sub.9/I.sub.AlN) of X-ray diffraction intensity (I.sub.Al.sub.2.sub.Y.sub.4.sub.O.sub.9) of Al.sub.2Y.sub.4O.sub.9 (201 plane) with respect to X-ray diffraction intensity (I.sub.AlN) of aluminum nitride (101 plane) is 0.002 to 0.03. According to the foregoing structure, there can be provided an aluminum nitride sintered body having a high thermal conductivity and excellent heat radiating property.