en Original Article Original Article <strong>Background:</strong> In most mammals, the testis is always maintained at a lower temperature than that in the abdomen, and exposure of the testis to body temperature causes degeneration of germ cells.<br> <strong>Objective:</strong> In this research, the long effect of heat exposure on sperm parameters and microstructure of mouse testis were investigated. Cryptorchid mouse were induced by exposure to abdominal heat.<br> <strong>Materials and Methods:</strong> Immature mice were anesthetized and a small incision was made in the abdominal skin, then fat pad at the upper end of testis was sutured to peritoneum. Weight of testis, spermatogenic cell numbers, tubular ectasis (rate of tubular lumen comparing to the thickness of germinal epithelium) as well as epididymal sperm parameters were measured.<br> <strong>Results:</strong> The results showed that spermatogenesis was arrested and testicular weights, seminiferouse tubular diameters and epididymal sperm parameters were significantly reduced in the bilateral undescended testis compared with unilateral undescended testis and the control mice. However, complete depletion of seminiferous tubules and absence of germ cells was not found in the animals.<br> <strong>Conclusion: </strong>In general, high temperature caused a decreased in all analyzed parameters except spermatogonial cell number probably due to the apoptosis and these changes significantly increase in bilateral groups compared with unilateral groups. We believe that the present model is a suitable tool for enrichment of spermatogonial stem cells, also it is useful for treatment of cryptorchidism and further biological research on spermatogenesis. Cryptorchidism, Testis, Spermatogonial stem cells 143 0 http://ijrm.ir/browse.php?a_code=A-10-549-255&slc_lang=en&sid=1 Forouzan Absalan No Department of Anatomical Sciences, School of Medical Sciences, Tehran, Iran Mansoureh Movahedin mansoure@modares.ac.ir Yes Department of Anatomical Sciences, School of Medical Sciences, Tehran, Iran Seyed Javad Mowla No Department of Genetics, School of Basic Sciences, Tarbiat Modares University, Tehran, Iran