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Background: In previous investigations, it has been clarified that electromagnetic fields (ELF) can cause some changes in cellular behavior. The aim of this prospective study was to investigate the effect of magnetic field (MF) on human sperm parameters of motility, morphology, and viability. Materials and Methods: Semen samples were collected from 12 fertile men, and were allowed to liquefy for 15-30 min. Each sample was then divided into two aliquots. The experimental samples were placed in the ELF, while the control one was left intact. The applied fields were pulsed with distance of 6 m/ sec and effective intensity of 1mT and different frequencies of 10, 25 and 45 Hz at different time intervals. The constant field intensity was 1mT in all experiments. Results: In frequency of 10Hz, an increase in quick motility of sperm (1.8 times) occurred after 4h however, slow motility was decreased by 40% after 2h. Also, the quick motility increased by 1.6 times in frequency 25 Hz after 4 h, while the MF had no effect on other sperm parameters. MF had no effect on any of sperm parameters in frequency of 40 Hz in 4 h. The stimulation ratio on the sperm viability was only significant at frequency of 10 Hz after 2 h after incubation. The sperm morphology was not influenced in any of the fields. Conclusion: This study reports the existence of certain frequency windows for the resonance of the effects of the MF on human spermatozoa. Rapid motility was significantly affected by the exposure of spermatozoa to MF, but sperm structural parameter had remained intact. Iran. J. Radiat. Res., 2011 9(3): 195-200