Aluminum nitride sintered body and method of preparing the same

Provided is an aluminum nitride sintered body excellent in thermal shock resistance and strength and applicable to a radiating substrate for a power module or a jig for semiconductor equipment employed under a strict heat cycle. An aluminum nitride sintered body obtained with a sintering aid of a rare earth element and an alkaline earth metal element contains 0.01 to 5 percent by weight of an alkaline earth metal element compound in terms of an oxide and 0.01 to 10 percent by weight of a rare earth element compound in terms of an oxide, and the amount of carbon remaining in the sintered body is controlled to 0.005 to 0.1 percent by weight, thereby suppressing grain growth and improving thermal shock resistance and strength of the sintered body.