High purity 18F was prepared by irradiating 1 g of lithium hydroxide or otherwise 0.14 g of enriched lithium carbonate containing 50% 6Li in the pneumatic tube of a TRIGA-II research reactor at a thermal neutron flux of 1.2×1012 n/cm2-sec. After cooling for 20 min, the irradiated lithium hydroxide was dissolved in distilled water. The resulting 13F was separated from the irradiated target by passing the lithium hydroxide solution successively through ion exchange columns of H-, OH- and H-forms. Use was also made of the Co- form ion exchange column in place of the H-form for the elimination of impurities. In the case of 6Li enriched lithium carbonate, the irradiated lithium carbonate was dissolved in hydrochloric acid, and ion exchange columns of Ag-, OH- and H-forms were used for purifying the 18F. The product 18F was obtained in the form of water containing 18F. The chemical yield for the purification of 18F was about 80 % and the final radioactive impurities were less than 1 ppm. A neutron activation me...