Background: The association between varicocele and male infertility has always been a subject of ongoing debate. Lactoferrin (LF) belongs to the transferrin family with iron-binding properties and exhibits many beneficial biological properties. The purpose of the current study was to assess seminal levels of LF in infertile oligoasthenoteratozoospermic (OAT) men with varicocele. Methods: Sixty-nine men were allocated into three groups; healthy fertile men (as controls) (n=20), infertile OAT men without varicocele (n=19), and infertile OAT men with varicocele (n=30). All men underwent history taking, genital examination, semen analysis, and determination levels of seminal LF by ELISA method. Statistical analysis was carried out using Kruskal-Wallis test followed by post-hoc analysis (Conover) for comparisons involving more than two groups, and the Mann-Whitney U test for comparisons between two groups. Spearman correlation test was used to assess the relationship between variables. The p>0.05 was set as statistically significant. Results: The median seminal LF level of the healthy fertile controls demonstrated significantly increased levels compared to both groups of infertile OAT men with or without varicocele (p<0.000001). The median seminal LF level of the infertile OAT men with varicocele grade III demonstrated a significant decrease compared to infertile OAT men with grade II (p=0.0057). Collectively, seminal LF levels exhibited significant positive correlations with sperm concentration, total sperm motility, and normal sperm morphology. Conclusion: LF can be an imperative seminal biomarker that decreases in infertile OAT men especially if associated with varicocele.