A composition comprising a radioactive fluorine-labeled amino acid compound is provided, which can be prevented from radiolysis. Disclosed is a composition which comprises a solution containing a radioactive fluorine-labeled amino acid compound as an effective ingredient, in which the pH value of the solution is kept at 2.0-5.9, more preferably 2.0-4.9 in order to inhibit radiolysis. Also, it is possible to further inhibit radiolysis by adding thereto a pharmaceutical additive capable of inhibiting radiolysis, such as a sugar, a sugar alcohol and a sugar lactone, whilst the pH is kept at 2.0-5.9.提供可以抑制放射線衰變的放射性氟標示氨基酸化合物的組成物。含有以放射性氟標示氨基酸化合物為有效成分的溶液所形成之組成物,該溶液的酸鹼值維持在2.0至5.9、更理想的是在2.0至4.9,藉此抑制放射線衰變。又,將酸鹼值維持在2.0至5.9,還可藉由添加糖、糖醇、葡糖二酸單內酯等抑制放射線衰變的藥品添加物,可以雙重地抑制放射線衰變。
