Appreciable radiation exposures certainly occur in the workers who handle radioiodine in biochemical research, nuclear medicine diagnostics with the development of nuclear industries. But in the case of nuclear accidents, the early medical treatment of radiation injury should be necessary but little was reported in Korea till now. Accordingly, to achieve basic data for protective roles and medical treatment of radiation injury, the present studies were carried out to evaluate the decontamination of radioiodine by the administration of the antithyroid drugs. The administration of sodium iodide and potassium iodide results in rapid excretion of radioiodine and reduction of the whole body retention than the saline-only group. Regarding thyroid protective effects, sodium iodide, potassium iodide results in rapid excretion of radioiodine and reduction of the whole body retention than the saline-only group. Regarding thyroid protective effects, sodium iodide, potassium iodide and saline were effected significant in order. In the control(saline) group, if administered with enough fluids, the whole body retention of radioiodine is reduced temporary shifts. But as far as radioprotective effects are concerned, saline was not more protective than the other groups. In conclusion, in case of nuclear accidents, if being administered sodium iodide and saline as quickly as possible, the radioprotective effects against the radiation hazard might be markedly increased in the internal contamination of radioiodine