In order to improve the stability of the labeled precursor compound of the radioactive fluorine element labeled compound, a stabilized composition containing a salt of the compound represented by the following chemical formula (2) as a main component is provided. [In the chemical formula, X 1 represents a hydrogen atom or a halogen atom, X 2 represents a fluorine atom or a nitrile group, and R 1 represents a substituted or unsubstituted alkyl sulfonyloxy group, or substituted Or unsubstituted aryl sulfonyloxy group (aryl sulfonyloxy group). 〕 By making the compound represented by the chemical formula (2) into a salt, the compound represented by the chemical formula (2) is stabilized and can be stored for a long period of time.為了提高放射性氟元素標示化合物的標示前驅物化合物的穩定性，提供含有下述化學式(2)所表示之化合物的鹽類作為主成分的穩定化組成物。〔化學式中，X1係表示氫原子或鹵素原子，X2係表示氟原子或腈基（nitrile group），R1係表示取代或未取代烷基磺醯氧基（alkyl sulfonyloxy group）、或取代或未取代芳基磺醯氧基（aryl sulfonyloxy group）。〕藉由將前述化學式(2)所表示之化合物做成鹽類，前述化學式(2)所表示之化合物穩定化，可以長期保存。
