The relationship between seminal leukocytes and semen parameters of the Arab stallions has been examined. A total of seventy ejaculates were collected from fourteen Arabian horses (5-19 years old). Semen samples were evaluated and viability indices were calculated at 30°C and 5°C storage conditions. The concentrations of total and differential leukocyte counts were estimated by direct cell count and using stained smears. Eighteen biochemical constituents of seminal plasma were analyzed and fertility of the stallions was retrospectively evaluated. The results of the study revealed that all ejaculates harbored leukocytes and aged stallions had the lowest leukocyte concentrations in their semen. Ejaculates with high leukocyte counts had lower initial sperm motility, number of sperm with normal morphology and sperm viability indices. Moreover, most of biochemical constituents of seminal plasma were detracted and fertility was low in ejaculates containing high concentrations of total leukocyte counts.