Asthenozoospermia is an important cause of male infertility. The mutations in sperm mitochondrial DNA (mtDNA) result in either functionless or malfunctioning some proteins, subsequently affecting sperm motility leading to asthenozoospermia. The purpose of this study was to investigate sperm mtDNA 4,977-bp deletion in infertile men with low sperm motility/immotile spermatozoa compared to healthy subjects with high sperm motility. Semen samples of 256 asthenozoospermic infertiles and 200 controls from northern Iran were collected. After extraction of spermatozoa total DNA, Gap-polymerase chain reaction (Gap-PCR) was performed. The deletion was observed in 85.93% of patients with asthenozoospermia compared with 14% in controls [OR=37.5397, 95% confidence interval=12.937-108.9276, p<.0001]. It is concluded that there is a strong association between sperm mtDNA 4,977-bp deletion and asthenozoospermia-induced infertility in the population examined. Large-scale mtDNA deletions in spermatozoa may induce bioenergetic disorders. Nevertheless, to validate our results broader research may be needed.