Background:KLC3 protein as a member of the kinesin light-chain protein family plays an important role in spermatogenesis, during formation of mitochondrial sheath in the mid piece of the sperm tail.Objective:This study for the first time aims to compare the expression of the KLC3 gene between fertile and infertile individuals.Materials and Methods:Semen samples were collected from 19 fertile individuals who were selected from embryo-donor volunteers and 57 infertile individuals who had abnormal sperm parameters according to world health organization criteria. Sperm parameters using computer assisted sperm analysis and the quantitative KLC3-gene expression using the real-time PCR method were measured. Results:Our results revealed a significant correlations between sperm concentration with relative expression of KLC3 only in infertile groups (r=0.45, p=0.00). A significant correlation was not found between KLC3 expression and sperm motility; however, the relative expression of KLC3 was significantly higher in asthenozoospermic compared to non-asthenozoospermic individuals.Conclusion:Low expression of KLC3 may result in improper function of midpiece, which has important function in sperm motility. The results of this study show that aberrant expression of KLC3 might be associated with phenomena like oligozoospermia and asthenozoospermia. This article is extracted from student’s thesis.