Abstract Background Amiodarone (AMD) is a benzofuran derivative, used in management of angina and refractory ventricular arrhythmia. Amiodarone has been associated with toxicity on many organs involving the lungs, thyroid gland, liver, eyes, skin, and nerves. Aim of the Work The aim of the current work was to study the structural and functional changes of the thyroid gland of adult male albino rats after exposure to the antiarrhythmic drug “Amiodarone”. Material and Methods Thirty adult male albino rats were used and divided into three groups. The first group included 10 rats which served as (control); 5 rats received distilled water orally and 5 rats received 3 ml of 0.6% methylcellulose. The second group included 10 rats used as (therapeutic dose treated group), which received 30 mg/Kg B.W. of amiodarone for 12 weeks by oral gavage, while the third group included 10 rats used as a (toxic dose treated group) which received 60 mg/Kg b. w. of amiodarone daily for 6 weeks by oral gavage. Serum concentration of tri-iodothyronine (T3), thyroxine (T4), thyroid stimulating hormone (TSH) were evaluated. Morphometric study and statistical analysis were done. Results Biochemical examination revealed statistical highly significant increase (P < 0.001) of serum (T4 & T3) with concomitant statistical highly significant decrease of (TSH) (P < 0.001). Histopathological examination of the thyroid tissues from the therapeutic dose treated group showed marked evidence of thyrotoxicosis in the form of microcystic follicular changes and peripheral scalloping, cellular degeneration with scanty cytoplasm and vesicular nuclei. These changes became more severe in toxic dose treated group in the form of thyroid tissue damage with hemorrhage and necrosis. Epithelial hyperplasia with atypical nuclear features were also detected. Conclusion Amiodarone had detrimental effects on the adult male albino rat’s thyroid tissue when administered either in the therapeutic or the toxic doses.