Background: Oxidative stress and reactive oxygen species (ROS) production are the important reasons for decreased sperm function during the cryopreservation process. Using of antioxidants can improve the cryo-survival of sperm act as a protection approach. Moreover, equilibration time is an impor- tant factor that could effect on the quality of thawed sperm. The aim of this study was to investigate the effects of Melatonin as an antioxidant on the quantitative parameters of asthenozoo- spermic men after freeze-thaw. Materials and Methods: Thirty semen samples were collected from asthenozoospermic patients who had been referred to the infertility treatment center of Amir-AL-Momenin Infertility Treatment Center, Arak city in 2023-2024. Each sample was divided into 3 groups: control (fresh), freeze (treated with cryo- protectant alone), and freeze+ melatonin (treated with cryo-pro- tectant+1 mM Melatonin solution). In the freezing groups, sam- ples were cryopreserved with human sperm freezing medium and rapid freezing method. In each sample, sperm mobility ac- cording to WHO criteria, sperm viability using eosin-nigrosin staining and sperm morphology using the Diff Quick kit were assessed. Data were analyzed statistically using the Repeated Measure Analysis method and Bonferroni post-hoc test. Results: Sperm motility, viability and morphology significant- ly decreased in the Freeze group compared to the control group (P<0.001). Whereas, in the Freeze+ Melatonin group a signifi- cant increase was observed in these parameters compared to the Freeze group (P<0.001). Conclusion: Our results showed that Melatonin as antioxidants in medium doses improved the sperm parameters in the asthe- nozoospermic men after freeze-thawing.
