fa Morphometry Morphometry Original Original <strong>Purpose</strong>: Semen freezing is an important technique in human infertility treatment in many different patients but it damages sperms. Low-power lasers are physical agents that have biostimulatory effects. In this study, low-power helium-neon laser&#39;s (16J/cm2, one time irradiation) effect on motility and ultrastructure of fresh and frozen-thawed human sperm were studied.<br> <strong>Materials and Methods</strong>: Thirty healthy men referring to Koassar Infertility Center in 2003 were chosen according to WHO&#39;s criteria. Semen samples were taken and divided into four different study groups. Sperm analysis was done before and after He-Ne laser irradiation, after thawing, and after irradiation on the thawed samples. Specimens were prepared for transmission electron microscopy (TEM) study. Sperm motility and its grades was analyzed using Wilcoxon test.<br> <strong>Results</strong>: Semen cryopreservation signicantly decreased the motility of the sperms (p=0.0001). Laser had no effect on fresh semens but increased the motility rate of frozen-thawed semens significantly (p=0.033). TEM study revealed that after laser irradiation, nuclear envelope was not only irregular and in some parts disrupted, but was also away from nucleus together with acrosome. Freeze-thawing caused morphological abnormalities.<br> <strong>Conclusion</strong>: Low power laser can increase sperm motility rate after freeze-thawing and may increase the fertility rate with frozen sperm. Sperm motility, Laser, Sperm cryopreservation, Ultrastructure 19 28 http://anatomyjournal.ir/browse.php?a_code=A-10-304-53&slc_lang=fa&sid=1 Amir Khosh Vaghti 10031947532846006789 10031947532846006789 No Mansoureh Movahedin 10031947532846006790 10031947532846006790 No Mohammad Bayat 10031947532846006791 10031947532846006791 Yes Cellular And Molecular Biology Research Center, Shaheed Beheshti Medical Sciences University, Tehran, Iran. Ahmad Hoseini 10031947532846006792 10031947532846006792 No Yoosef Sadeghi 10031947532846006793 10031947532846006793 No Fateme Sadat Rezaei 10031947532846006794 10031947532846006794 No