The present invention relates to a method for preparing a radiopharmaceutical and, specifically, to a method for preparing an organic fluoride-aliphatic compound usable as a radiopharmaceutical, to a method for purifying the prepared organic fluoride-aliphatic compound, and to a method for preparing a radiopharmaceutical using a cassette comprising a backdraft preventing reaction container. According to the present invention, the organic fluoride-aliphatic compound can be prepared and purified through even a simple process at high yield, high efficiency, and high purity, and the radiopharmaceutical can be safely prepared without damage to a synthetic apparatus.
