PURPOSE: To obtain the objective compound in high yield even in a relatively short time in obtaining the title compound by reacting a perfluoroalkyl iodide with bromine by carrying out halogen substitution reaction under irradiation with light rays in the presence of a photosensitizer.

CONSTITUTION: A perfluoroalkyl iodide and bromine are subjected to halogen substitution reaction under irradiation with light rays in the presence of preferably ≤ about 10mol%, preferably about 5-1mol% based on the perfluoroalkyl iodide of a photosensitizer, preferably a photosensitizer in triplet state such as benzophenone, pyrene, anthracene or phenothiazine to give a perfluoroalkyl bromide having X-ray shielding ability especially useful as X-ray contrast medium in a relatively short time, to be concrete, in high yield even by reaction for about 24 hours.