Green tea is known for its antioxidant and anti-carcinogenic effects. However, its effects on the thyroid gland have not been adequately investigated. The present investigation has been designed to evaluate the effect of green tea aqueous extract on the thyrotoxicity of lead acetate in adult male Wistar rats. Four groups of rats, 10 animals each, were used in this study (control, lead acetate, lead acetate and green tea aqueous extract and green tea aqueous extract alone). Rats received a daily dose of lead acetate (100 mg/kg) by stomach tube for 30 days. Green tea aqueous extract at a dose of 0.5g/100 ml was provided in the drinking water ad-libitum for the same time. Administration of lead acetate markedly affected thyroid functions in the treated group compared to the control group. Co-administration of lead acetate and green tea aqueous extract attenuated the toxic and inhibitory effect of lead acetate on serum levels of T₃, T₄ and TSH. These results were confirmed by microscopic examination of the cellular structure of the thyroid gland of treated rats. Lead acetate caused cystic dilatation with flattened lining epithelium in the follicles. Lead acetate caused significant DNA damage as indicated by visible tail lengths in a standard alkaline Comet assay. However, the thyroid damage and DNA migration were reduced in animals that received lead acetate and green tea aqueous extract concomitantly. In conclusion, the present study suggested that green tea aqueous extract may be useful in reducing the thyroid damage due to lead acetate toxicity.