The objectives of the present study were to investigate the prevalence of histologic thyroids lesions and the respective thyroid hormones changes of ewes in an endemic goiter region and to find out any impact of this condition on the fetal thyroid structures and serum thyroid hormones. In the present study a total number of 100 pregnant ewes and their fetuses slaughtered at slaughterhouse were selected for the study. The sera were prepared from the jugular vein blood of ewes and fetuses umbilical cords. The ewes and fetuses thyroids subjected to histopathological examination and radioimmunoassay procedure was used for sera T3 and T4 assay. The results showed a high prevalence of thyroid lesions in ewes and their fetuses. The different kinds of lesions including cysts, follicular hyperplasia, hemorrhage and inflammation were seen in ewes. In the fetuses thyroid structural changes were cysts resemble structures; hemorrhage and hyperemia. Mean T4 concentration was significantly higher in the ewes with pathologic thyroid compared to normal animals. However, there was not any significant difference between pathologic and normal ewes’ thyroids on serum T3. Although, existence of lesions on fetal thyroids did not affect the serum concentrations of T4 and T3, there was a significant correlation between T4 and T3 serum concentrations of fetuses and their age. In conclusion, the significant prevalence of fetal and maternal thyroid pathological changes in the endemic goiter region raises a question about probable congenital source of these variations. The thyroid lesions significantly influenced the functions of mothers' gland but not fetuses.