The present invention relates to a method for synthesizing a radiopharmaceutical using a cartridge, which makes it possible to carry out several steps of reaction required for synthesizing a radiopharmaceutical in the cartridge filled with a polymer. A method for synthesizing a radiopharmaceutical according to the present invention enables each step's reaction to be carried out with the solution confined in the cartridge so as not to flow out, thus being simplified compared to the conventional methods for synthesizing radiopharmaceuticals, and expediting the synthesis thereof.