A simple method for producing a clinically applicable radiopharmaceutical composition containing 1-(2,2-dihydroxymethyl-3-[18F]fluoropropyl)-2-nitroimidazole ([18F]DiFA) or a salt thereof as an active ingredient, is provided which includes a synthesis step of obtaining a crude product of [18F]DiFA from a labeling precursor compound for [18F]DiFA; and a purification step of purifying the crude product, in which the purification step includes purifying [18F]DiFA using two or more different types of reverse phase solid phase extraction cartridges.