A process for the production of [.sup.18F]-TAFDG can produce [.sup.18F]-TAFDG in a high radiofluorination yield. A process for the production of an organic compound labeled with radioactive fluorine includes the steps of preparing a reaction solution containing [.sup.18F]fluoride ions, a phase transfer catalyst, potassium ions, 1,3,4,6-tetra-O-acetyl-2-O-trifluoromethanesulfonyl-.beta.-D-mannopyranos- e as a labeling precursor compound and a solvent, and giving a reaction condition to the reaction solution to obtain 1,3,4,6-tetra-O-acetyl-2-[.sup.18F]fluoro-2-deoxyglucose, in which the solvent contains water.