OBJECTIVE To study the mechanism of the disorder of thyroid hormone metabolism resulted from iodine excess in order to seek suitable selenium intervention dosage. METHODS 140 Balb/c mice were randomly divided into seven groups, the normal control group, the excessive iodine group (drank the water containing potassium iodate 3000 microg/L) and five selenium intervention groups (drank the water containing 3000 microg/L of potassium iodate and 0.1, 0.2, 0.3, 0.4 and 0.5 mg/L of selenium). All of the mice were cultivated for 16 weeks and the thyroid hormone in plasma were assayed by radioimmunoassay. The iodine in urine and thyroid were analyzed by Cer-Arsenite colormetric method. The activities of glutathione peroxidase, superoxide dismutase and thyroid peroxidase and the level of malondialdehyde in thyroid were analyzed. RESULTS The level of thyroid hormone of selenium intervention groups had no significant difference with that of normal control group (P > 0.05). Compared with excessive iodine group, the iodine in thyroid of 0.2 mg/L selenium intervention group increased significantly (P < 0.05). Compared with the normal control group, the activities of glutathione peroxidase and superoxide dismutase and the level of malondialdehyde of 0.2-0.3 mg/L selenium intervention groups in thyroid were not significantly different. Compared with the normal control group, the activity of thyroid peroxidase of 0.1-0.3 mg/L selenium intervention groups were not significantly different. CONCLUSIONS The results indicated that the optimal dose of selenium could restrain the disorder of thyroid hormone metabolism induced by excessive iodine in mice.