This study was conducted to evaluate the effects of ascorbic acid and sialic acid, separately, on the triple ATPase enzyme activities (N2+/K+- Mg2+-ATPase, Mg2+-ATPase and Ca2+-Mg2+-ATPase) of washed spermatozoa in 34 infertile and 25 fertile men. When enzyme activities of the two groups were compared, the values of the fertile group were higher, which was statistically significant. After processing of the fertile group spermatozoa with ascorbic acid, activity of NA+/K+-Mg2+-ATPase was lowered. Meanwhile sialic acid decreased activities of NA+/K+-Mg2+-ATP-ase and Ca2+- Mg2+-ATPase. There was no significant change of enzyme activities in the infertile group after application of ascorbic acid/sialic acid. Ascorbic acid/sialic acid which are normally found in seminal plasma have important role in the physiology of spermatozoa and fertilization. Sialic acid showed some inhibitory effects on the activities of NA+/K+-Mg2+-ATPase and Ca2+-Mg2+-ATPase of washed spermatozoa from the fertile group, while ascorbic acid showed same effect on the activity of NA+/K+-Mg2+-ATP-ase. It would appear that some factors in the seminal plasma of the fertile men to compensate the inhibitory effects of ascorbic acid and sialic acid on these enzymes.