The present study aimed to investigate the effects of vitamin B(12) supplementation on standard bovine semen quality parameters and anti-oxidative enzyme activities. Vitamin B(12) was supplemented at concentrations of 1.25, 2.5, 3.75 and 5.0 mg/ml to bovine semen cryoprotective medium. The results indicated that the motility and straight line velocity, curvilinear velocity, mean coefficient, velocity of the average path values of sperm supplemented with 2.50 mg/ml vitamin B(12) were significantly higher than that of other groups (p<0.05). No significant difference was observed for linearity index, lateral head displacement values and the percentage of grade A spermatozoa between the extenders containing 2.50 and 3.75 mg/ml vitamin B(12) (p>0.05). The percentages of acrosome-intact and plasma membrane-intact spermatozoa were significantly improved (p<0.05) by supplementing with 2.50 mg/ml vitamin B(12) . The results of biochemical assay revealed that vitamin B(12) supplementation did not cause significant changes in superoxide dismutase levels compared with control (p>0.05). However, the catalase levels were higher in the treatment supplemented with vitamin B(12) at 2.50 mg/ml, when compared with other groups (p<0.05). The extender supplemented with vitamin B(12) significantly decreased glutathione peroxidase activity compared with the control (p<0.05). The supplementation of 3.75 mg/ml vitamin B(12) caused the highest value of glutathione reductase activity, compared with other groups (p<0.05). In conclusion, the extender supplemented with vitamin B(12) could reduce the oxidative stress provoked by freezing-thawing and improve bovine semen quality. Further studies are required to obtain more concrete results on the determination of lipid peroxidation and antioxidant capacities of vitamin B(12) in cryopreserved bovine semen.