en Original Article Original Article <strong>Background:</strong> Leptin is a polypeptide hormone secreted by white adipose tissue in proportion to body energy. Although the participation of leptin in female reproduction is well established any role in male reproductive function is at best tenuous.<br> <strong>Objective:</strong> The objective of this study was to compare the leptin concentration in human seminal plasma and then the relationships between seminal leptin and semen parameters were evaluated.<br> <strong>Materials and Methods: </strong>Semen samples were provided from 71 men; normozoospermic (n=22) asthenozoospermic (n=31) and oligoasthenozoospermic (n=18) referring to Jichi Medical University Hospital for in vitro fertilization-embryo transfer (IVF-ET) treatment. After liquefaction all sperm specimens were evaluated for sperm parameters and motility characteristics by computer-assisted semen analysis (CASA) system. After semen analysis concentrations of leptin in seminal plasma of all groups were measured by ELISA.<br> <strong>Results: </strong>The mean concentrations of leptin in seminal plasma of normozoospermic asthenozoospermic and oligoasthenozoospermic men were 0.75+/-0.09 ng/ml 0.8+/-0.14 ng/ml and 0.8+/-0.15 ng/ml respectively. A trend was observed for a lower leptin concentration in seminal plasma of normozoospermic men compared with asthenozoospermic and oligoasthenozoospermic men. There was a significant negative correlation between seminal plasma leptin concentration with sperm motility&nbsp;(p<0.05) and Curvilinear Velocity of the sperm kinetic parameter (p<0.01).<br> <strong>Conclusion:</strong> It was demonstrated that there was a significant correlation between seminal leptin with the sperm motility.<br> &nbsp; Leptin, Sperm quality, Male infertility, Seminal plasma, Fertilization rate. 95 100 http://ijrm.ir/browse.php?a_code=A-10-549-186&slc_lang=en&sid=1 Seyed Gholam Ali Jorsaraei alijorsara@yahoo.com Yes Fatemeh Zahra Infertility and Health Reproductive Research Center, Babol University of Medical Sciences, Babol, Iran Hiroaki Shibahara No Department of Obstetrics and Gynecology, School of Medicine, Jichi Medical University, Tochigi, Japan Ayustawati No Department of Obstetrics and Gynecology, School of Medicine, Jichi Medical University, Tochigi, Japan Yuki Hirano No Department of Obstetrics and Gynecology, School of Medicine, Jichi Medical University, Tochigi, Japan Tatsuya Suzuki No Department of Obstetrics and Gynecology, School of Medicine, Jichi Medical University, Tochigi, Japan Eisa Tahmasbpour Marzony No Department of Biology, Faculty of Basic Science, Azad University of Sari, Sari, Iran Mahtab Zainalzadeh No Fatemeh Zahra Infertility and Health Reproductive Research Center, Babol University of Medical Sciences, Babol, Iran Mitsuaki Suzuki No Department of Obstetrics and Gynecology, School of Medicine, Jichi Medical University, Tochigi, Japan