BACKGROUND: The purpose of this study was to examine histological changes of testes induced by hindlimb unloading & position change of testis in mature adult male rats. METHOD: Eight month old (390~410g) 36 male Sprague-Dawley rats were weight-matched assigned to Ground Control (GC), Hindlimb Unloading (HU), Hindlimb Unloading & Testis Tie(HUT), Intra-abdominal Testis(IAT) for 24 days. Daily body weight was watched for status of animal. Testis weight, Seminiferous Tubule Diameter(STD), Seminiferous Tubule Perimeter(STP), Serminiferous Tubule Area(STA), Sertori Cell Height(SCH) were examined in each group. RESULTS: The 24-day hindlimb unloading of HU, HUT and IAT showed no significant change of body weight compared to GC. HUT maintained the weights, STD, STP, STA, SCH of their testes as GC while HU, IAT had significantly decreased the weights, STD, STP, STA of their testes. CONCLUSION: These results support that hindlimb unloading experiment induces serious morphological changes of testes. Therefore, on the hindlimb unloading experiment, IAT should be avoid or the effect of IAT should be correct. It will be necessary to study the pure effect of hindlimb unloading without IAT on the musculoskeltal system and so on which are associated with testosterone.