Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 52 7 2014 07 15 496 504 EN Bagher Minaii Department of Anatomy, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Ardeshir Moayeri Department of Anatomy, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. AND Department of Anatomy, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran. Saeed Shokri Department of Anatomy, Faculty of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran. Mehryar Habibi Roudkenar Blood Transfusion Research Center, High Institute for Research and Education in Transfusion Medicine, Tehran, Iran. Taghi Golmohammadi Department of Clinical Biochemistry, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Fatemeh Malek Department of Anatomy, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Mohammad Barbarestani Department of Anatomy, Faculty of Medicine, Tehran University of Medical Sciences, Tehran, Iran. 2015 10 11 This study investigates the effects of melatonin on the sperm quality and testis weight after the combination of swimming exercise and nandrolone decanoate (DECA). Two groups of male Wistar rats were treated for eight weeks as follows; group A consist of CO (control), Sham, N (DECA), S (swimming) and NS (DECA plus swimming); and group B: Sham M (sham melatonin), M (melatonin), MN (melatonin plus DECA), MS (melatonin plus swimming), MNS (melatonin, DECA plus swimming). The motility of sperm was significantly improved in melatonin groups in comparison to N, S and NS groups (P≤0.05).  The left testes weight was decreased in N, NS and MNS groups, and the right testes weight was decreased in N,S,NS, MS and MNS groups in compare with the control group. This study concluded that melatonin probably could improve the sperm motility and sex organs weight after the combination of DECA and exercise. https://acta.tums.ac.ir/index.php/acta/article/view/4585 https://acta.tums.ac.ir/index.php/acta/article/download/4585/4500