PURPOSE: To easily obtain high temp. stability, electric insulating property, high corrosion resistance, high thermal conductivity, etc., by using a boron nitride powder having sepcified crystallization index as a part or whole of the start source material.

CONSTITUTION: An org. binder, ethyl alcohol, etc., are added to a boron nitride powder having ≥20 crystallization index defined by the formula, mixed, dried, granulated, and press-formed into a formed body. This formed body is heated in a nitriding atmosphere at about 2000°C for 2 hours to obtain a boron nitride sintered body. In the formula, area[(100)+(101)] and area [(102)] represent the sum of diffraction integrated intensities of (100) and (101) and the diffraction integrated intensity of (102), respectively, in X-ray diffraction.