The aim of this study was to determine the effects of curcumin and dithioerythritol added into bull semen extender on sperm parameters, lipid peroxidation, total glutathione and antioxidant potential levels of bull spermatozoa following the freeze/thawing process. Twenty-seven ejaculates obtained from three bulls were included in the study. Each ejaculate that was splitted into five equal groups and diluted in a Tris-based extender containing curcumin (0.5 and 2mm), dithioerythritol (0.5 and 2mm) and no additive (control) was cooled to 5°C and frozen in 0.25-ml French straws. The extender supplemented with 0.5mm dose of curcumin led to lower percentage of total abnormality (20.40±2.36%) when compared to the control (30.60±1.47%, P<0.05). Curcumin and dithioerythritol at 0.5mm provided a greater protective effect in the membrane functional integrity (54.40±2.09% and 50.00±2.68%), in comparison with control (37.20±1.77%, P<0.001). Supplementation with antioxidants did not significantly affect the lipid peroxidation and antioxidant potential levels, while the maintenance of total glutathione levels in curcumin 0.5mm was demonstrated to be higher than that of control, following the freeze/thawing (P<0.05). Supplementation with these antioxidants prior to the cryopreservation process may be recommended to facilitate the enhancement of sperm cryopreservation techniques. © 2011 Blackwell Verlag GmbH.