Abstract: Objective: To investigate the impact of thyroid hormones on testosterone secretion in rat Leydig cells Methods: The rat′s Leydig cells were cultured and exposed to a series of concentrations of T 3 （0.μg/ml,0.01 μg/ml,0.1 μg/ml,1 and 10.μg/ml） Basal and challenged testosterone levels were measured The distinction of Leydig cells′ secretion in vitro was evaluated between different thyroid function groups Results: There were no changes in testosterone levels when normal Leydig cells were exposed to T 3 directly However,an impaired secretion ability of testosterone in basal or in stimulated conditions was found in the Leydig cells from both hyper and hypo thyroidism rats （P＜0.001） Conclusion: The Leydig cells from normal rats had no response to thyroid hormone in vitro,but those from hyper or hypo thyroxinemia rats showed impaired testosterone secretion.