Abstract: Here is reported a novel method of labelling halogenated hydrocarbon with 125I and 77Br in the presence of crown ether Dicyclohexyl 18-crown-6 (DCC), which is used as a solvent to dissolve the substrate and alkali halide. The unsolvated and "naked radioactive anion" has more reactive ability than the anion in the conventional condition.The isotopic exchange between n-octylbromide and 125I iodide or others was performed in the presence of DCC. The time dependence of labelling of n-octylbromide with 125I and 77Br, temperature dependence on the labelling percentage, DCC amounts dependence on the labelling percentage, and carrier amount KI on the percentage of labelling were studied. Our results show that there is a big crown ether effect in the halogen atom exchange or isotopic exchange between the halogsnated hydrocarbon and radioactive halide in relatively low temperature. It may be expected that this method could be used in the labelling of halogen atom exchange process, particularly in the labelling of long chain fatty acid with 18F.