PURPOSE: To obtain a high-density and high-hardness abrasive grain by giving thereto a structure containing a specified amount of manganese/alumina spinel.

CONSTITUTION: This grain is one having a spinel phase comprising 3-10wt.% (in terms of the manganese atoms) manganese oxide and alumina and having a Vickers hardness (under a load of 500g) of 16GPa or above. This grain is produced by a method comprising adding 3-10wt.%, (in terms of the manganese atoms based on the alumina) manganese nitrate solution to a sol of (pseudo) boemite to form a gel, drying this gel at 80-200°C under conditions in which the formula (wherein T (°C) is the temperature and t is the holding time at that temperature) has a value of 200 or above, calcining and sintering the dried product, or by a method comprising impregnating a calcined alumina gel with 3-10wt.% (in terms of the manganese atoms based on the alumina) manganese nitrate solution, drying the product of impregnation under the same conditions as those of the above method and sintering the dried product.