A hexagonally crystalline boron nitride containing water- soluble boron containing impurity in such a magnitude that amount of boron to be contained in an extract after boiling at 100° C. of pure water is less than or equal to 100 &mgr;g/g-BN. In order to purify the boron nitride, a purification process is carried out according to the steps of preparing fine particles of boron nitride powder; dispersing the boron nitride powder in a disperser and stirred for a given period of time for removing water-soluble boron containing impurity; and drying the boron nitride in an atmosphere, in which vapor pressure is maintained lower than or equal to 10 mmHG and/or the process temperature is maintained lower than or equal to 100° C.
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