The aim of this study was to determine the effects of the antioxidants superoxide dismutase (SOD), glutathione peroxidase (GPx) and butylated hydroxytoluene (BHT) on microscopic semen parameters and lipid peroxidation following the freeze-thawing of bull semen. Ejaculates were collected from five Holstein bulls and pooled at 37^oC. The semen samples were diluted with a CEY extender containing additives including 100 U and 200 U SOD/ml, 50 U or 100 U GPx/ml and an extender containing no antioxidants (control) and stored in liquid nitrogen. The pooled ejaculates were then diluted with CEY or a Tris (hydroxymethyl) aminomethane (TRIS)-based extender (TEY) alone or with added 0.5, 1.0, 2.0 or 4.0 mM BHT, and the routine semen evaluation was conducted. The lowest production of malondialdehyde (MDA) was obtained by addition of 100 U SOD/ml, 0.5 and 1 mM BHT to CEY extender compared with the other groups. Sperm viability and motility was significantly higher when 0.5, 1 mM BHT and 100 U SOD/ml were added in CEY extender. The highest sperm viability was achieved by addition of 50 U GPx/ml to CEY extender. In addition, sperm motility was significantly higher in samples extended in Tris-egg yolk (TEY) with 0.5 mM BHT compared with the control group. The results suggest that CEY extender can be improved with the addition of SOD and BHT.