en Original Article Original Article <strong>Background: </strong>During the detorsion of a torsioned ovary, oxidant agents are released and melatonin as an antioxidant can reduce ischemia. We studied the histopathological changes after using melatonin on experimental torsioned ovary in cat.<br> <strong>Objective:</strong> The aim of this experimental study was to investigate the effects of Melatonin on histopathological changes in torsion &ndash; detorsion injury in cat ovary.<br> <strong>Materials and Methods:</strong> An adnexal torsion &ndash; detorsion model was created by using 20 adult cats randomly divided equally in to 2 groups of Saline and Melatonin. Ischemia was induced by iathrogenic 360&deg; clockwise torsion of the cat adnex for 3 hr. Reperfusion was achieved for 3 hr. Melatonin or saline were injected intra peritoneally (10mg/kg) 30 min before ovarian detorsion in both groups. After 3 hr of ovarian detorsion, ovarian tissue was removed and fixed in 10% formalin solution, embedded in paraffin and evaluated for ischemic indices.<br> <strong>Results:</strong> Histological examination showed a significant improvement in ovarian morphology in the melatonin treated cats. Edema and vasoconstriction in saline group were more severe than Melatonin group (p-value = 0.009). Hemorrhage and leukocyte infiltration were also more obvious in saline group (p-value 0.0018)<br> <strong>Conclusion:</strong> Our results demonstrated that Melatonin administration reduced ovarian histopathological damage due to oxidative injury associated with torsion. Melatonin, Saline, Ischemia, Reperfusion, Cat. 177 181 http://ijrm.ir/browse.php?a_code=A-10-549-307&slc_lang=en&sid=1 Fatemeh Mostajeran mostajeran@med.mui.ac.ir Yes Department of Obstetric and Gynecology, Isfahan University of Medical Sciences, Isfahan, Iran Maryam Naderi No Department of Obstetric and Gynecology, Isfahan University of Medical Sciences, Isfahan, Iran Shahriar Adibi No Torabienejad Dental Research Center, Isfahan University