Spermatozoa are regarded as immunologically foreign cells in the female body. Macrophages are one of the predominant leukocytes that involve in the immunoprotection of the female reproductive tract wherein the spermatozoa have to go across for fertilization. The mechanism of the immunoprotection of sperm is not well known. Glycodelin-A and glycodelin-S are uterus- and seminal plasma-derived immunomodulatory glycoproteins, respectively. The two isoforms of glycodelin share the same protein core but differ in N-glycosylation. The aim of this study is to determine the biological activity of glycodelin-A and -S on human macrophages and its correlation with sperm fertilizing ability in terms of motility. Co-culture of spermatozoa with macrophages reduced sperm motility, but this effect was not observed when macrophages were pre-treated with glycodelin-A. The latter observation was due to reduction of TNF-α secretion from the macrophages. Removal of sialic acid from glycodelin-A eliminated its protective effect on sperm motility, indicating that the protective action of glycodelin-A depends on the present of sialic acid. Consistently, no protective activity was observed with glycodelin-S that lacks terminal sialic acid residues. To conclude, the results from this study provide the first evidence that glycodelin-A diminished the adverse effect of macrophage co-culture on sperm motility. The described action of glycodelin-A may play a role in the mechanisms by which maternal immune attack on spermatozoa is suppressed in the female reproductive tract.