Abstract: A new rapid labelling method is reported for the preparation of ω-radiohalogenated fatty acids in a medium of crown ether. A homogeneous mixture of ω-Br-stearic acid and 18-crown-6 is placed in an open glass tube containing dry Na82Br orNa125I without addition of carrier. The isotopic and non-isotopic exchange reaction are carried out at 80℃. Using this method we have prepared ω-125I-stearic acid and ω-82Br-stearic acid. The radiochemical yields are about 88% after 20 minutes, which shows that this method is more rapid and efficient than other methods. Kinetics of these reactions are also studied.