en Original Article Original Article <strong>Background:</strong> Various approaches have been used in the attempts to improve the quality of frozen&ndash;thawed mouse sperms. According to literatures, it seems that hyaluronic acid (HA) has an important role on the permeability and motility of sperms and their interaction with gametes.<br> <strong>Objective:</strong> For evaluation of HA supplementation on sperm characteristics and fertilization capability, we investigated the effect of different doses of HA on mouse sperm morphology, motility, vitality and fertilization capability after freezing and thawing.<br> <strong>Materials and Methods: </strong>The cauda epididymes was removed from 6 male mice with aseptic method. The sperm samples were frozen in 1.8 ml cryotubes with 18% raffinose and 3% skimmed milk containing cryo-protectant solution. HA at the concentration of 750, 1000 or 1250 &micro;g/ml was supplemented to frozen-thawed sperms. Sperm motility was measured with microscope, and fertilization rate was evaluated after routine IVF by counting the fertilized oocytes. For sperm morphology, papaniclau staining was used while; Eosin B was used for the assessment of sperm viability rate.<br> <strong>Results: </strong>HA supplementation (750 &micro;g<span dir="RTL">/</span>ml) improved motility parameters (<em>p</em> < 0.05) and increased the fertility rate (<em>p</em> < 0.05). The effect of 1,000 &micro;g<span dir="RTL">/</span>ml HA was also positive on the sperms. But 1,250 &micro;g<span dir="RTL">/</span>ml HA had negative effect on above mentioned characteristic. On the other hand, none of these doses had any effect on sperm morphology.<br> <strong>Conclusion:</strong> The dose of 750 &micro;g<span dir="RTL">/</span>ml of HA has the greatest effect on the motility, vitality and fertility rate of sperms after cryopreservation.<br> <br> &nbsp; Hyaluronic acid (HA), Cryopreservation, In vitro fertilization (IVF), Sperm parameters. 45 0 http://ijrm.ir/browse.php?a_code=A-10-549-276&slc_lang=en&sid=1 Mitra Bakhtiari No Department of Anatomy and Vali-e-Asr Reproductive Health Research Center, Faculty of Medicine, Medical Sciences/University of Tehran, Tehran, Iran Aligholi Sobhani sobhania@tums.ac.ir Yes Department of Anatomy and Vali-e-Asr Reproductive Health Research Center, Faculty of Medicine, Medical Sciences/University of Tehran, Tehran, Iran Mohammad Akbari No Department of Anatomy and Vali-e-Asr Reproductive Health Research Center, Faculty of Medicine, Medical Sciences/University of Tehran, Tehran, Iran Parichehr Pasbakhsh No Department of Anatomy and Vali-e-Asr Reproductive Health Research Center, Faculty of Medicine, Medical Sciences/University of Tehran, Tehran, Iran Mehdi Abbasi No Department of Anatomy and Vali-e-Asr Reproductive Health Research Center, Faculty of Medicine, Medical Sciences/University of Tehran, Tehran, Iran Azim Hedayatpoor No Department of Anatomy and Vali-e-Asr Reproductive Health Research Center, Faculty of Medicine, Medical Sciences/University of Tehran, Tehran, Iran Fardin Amidi No Department of Anatomy, Faculty of Medicine, Sanandaj University of Medical Sciences, Sanandaj, Iran Feridoon Sargolzaei No Department of Anatomy, Faculty of Medicine, Zahedan University of Medical Sciences, Zahedan, Iran