A series of factorially arranged six experiments were conducted to study the effects of twenty- eight antioxidants on maintenance of viability of stallion spermatozoa in a chemically defined stallion semen extender (Tris egg yolk) at 5 °C and 196°C. Sixty-nine ejaculates were collected from nineteen Arabian horses (5-21 years old). In four preliminary experiments (n=40), the appropriate concentrations of the best four antioxidants in terms of sperm viability at 5°C were selected. In the fifth experiment (n= 19), a comparison between the selected antioxidants and a mixture (cocktail) of them was studied on bases of sperm viability, sperm morphology and changes in levels of extracellular aspartate and alanine aminotransferase. The sixth experiment (n = 10) was carried out for using the best antioxidant that could improve the viability of frozen – thawed stallion spermatozoa. Results of the pre- liminary experiments revealed that four antioxidants viz., sodium pyruvate, sodium thiosulfate, bovine serum albumin and zinc chloride could induce beneficial effect on viability of stallion spermatozoa. A mixture of the previous four antioxidants was most effective for improving spermatozoal morphology and viability at 5°C. Extracellular level of alanine aminotransferase was minimal on using the mixture of antioxidants after cold storage of spermatozoa for 72 hours at 5 °C. The results of frozen thawed stallion se- men revealed that viability indices were superior when using the mixture of antioxidants specially when caffeine was added to the thawing solution.