The invention relates to a method for producing aluminum oxide having a low calcium content wherein (1) red alpha and/or gamma aluminum oxide having a total content of calcium in the range from 50 to 2,000 ppm, relative to the raw alpha and/or gamma aluminum oxide, is mixed with an aqueous solution or suspension comprising the compounds selected from the group of inorganic acids, organic acids and complexing agents, (2) the mixture from step (1) is mixed with a flocculating agent, (3) the solid is separated from the liquid from the mixture from step (2), (4) the separated solid is mixed with water in the presence or absence of a flocculating agent, (5) the solid is separated from the liquid from the mixture from step (4), (6) steps (4) and (5) are repeated once or repeatedly as applicable, (7) the separated solid is dried as applicable, after addition of further compounds as applicable.