The effects of supplementing selenium on thyroid hormone metabolism were studied on mice with excessive iodine exposure. The serum concentrations of thyroxine (T4) and triiodothyronine (T3) and the activities of iodothyronine 5\' and 5-deiodinase (D2, D3) were measured in the brain of filial mice to study the influence of selenium on thyroid hormone metabolism. Measurements were carried out on postnatal day 0, 14, and 28. It was found that selenium supplementation alleviated the adverse effects of excessive iodine on progeny. The serum TT4 level as well as TT4 and TT3 concentrations and D3 activity in cerebrum of progeny decreased, whereas D2 activity increased in the cerebrum of progeny on postnatal day 0 and 14. Selenium supplementation exerted some favorable effects on thyroid hormone metabolism in cerebrum of progeny of dam with excessive iodine intake.