Background: The lactate dehydrogenase C4 (LDH-C4) isoenzyme is an important enzyme involved in metabolic processes that are needed for spermatogenesis and sperm motility. Objectives: This study aims to assess the activity and kinetic parameters (maximum velocity, Vmax and Michaelis constant, Km) of LDH-C4 in fertile and infertile (azoospermia and oligospermia) men in Baghdad City, Iraq. Methods: A total of 120 participants (80 infertile and 40 healthy fertile men) were included in the current study. The patients were sub-grouped into: 40 infertile men with oligospermia, and 40 infertile men with azoospermia. The oligospermia patients were further subdivided into subgroups based on sperm count and motility. Semen samples were obtained by masturbation after 3-5 days abstain for seminal fluid analysis. The microscopic test included the assessment of the count, motility and morphology of the sperms. In addition, the coulometric assay was used for measuring the activity and kinetic parameters of LDH-C4 enzyme. Results: The activity of LDH-C4 is significantly higher in fertile men when compared with infertile subjects (fertile: 403.13±189.90, oligospermia: 110.01±58.13, azoospermia: 39.06±28.15; p≤0.01). Statistically significant differences in LDH-C4 activity were also noted among patients with oligospermia based on sperms count and motility. Based on sperms’ count in patients with oligospermia, a significantly higher LDH-C4 activity (p≤0.01) was noted in those with higher sperm count (10-15 million/ml) when compared to others who have lesser count. Significant elevation in enzyme activity (p≤0.01) was also observed in oligospermia patients with higher percentages of motile sperms when compared with others who have fewer percentages of motile sperms. Moreover, the highest Vmax value (0.483 mmol/L.min) and the lowest Km value (0.39 mmol/L.min) were recorded in fertile men. While, the lowest Vmax value (0.174 mmol/L.min) and the lowest Km value (0.75 mmol/L.min) were detected in azoospermia patients. Conclusions: Our results suggest that LDH-C4 is essential for the count and motility of sperm and may be considered as a therapeutic approach for infertility.