The object is to provide a method of manufacturing a fraction containing nobiletin and tangeretin at high concentrations, which is excellent in terms of safety, economic efficiency, and the potential for industrialization. The method includes (1-1) a step of treating citrus fruit with hot water to obtain a hot water-treated product; (1-2) a step of drying the hot water-treated product to obtain a dried product; (1-3) a step of treating the dried product with a solvent capable of dissolving nobiletin and tangeretin to obtain a nobiletin and tangeretin solution; (3) a step of concentrating and/or drying the nobiletin and tangeretin solution to obtain a nobiletin and tangeretin concentrate; and (4) a step of treating the nobiletin and tangeretin concentrate with a dilute alkali to obtain a composition containing nobiletin and tangeretin as an insoluble component, and by a composition containing nobiletin and tangeretin at high concentrations manufactured by the method.