To obtain a high-strength cBN abrasive grain with high heat resistance, suitable as abrasive grain for a whetstone intended for the heavy grinding or high-speed grinding of iron-based materials.

This abrasive grain is a polycrystalline substance consisting of cBN crystallites of ≤1 μm in grain size; wherein the ratio of the X-ray diffraction intensity (I220) of each cBN (220)-plane to the X-ray diffraction intensity (I111) of (111)-plane of the polycrystalline substance, namely I220/I111 is ≥0.1; and the polycrystalline substance is preferably incorporated with 0.01-0.5 vol.% of compressed-type hBN.