The objective of this study was to investigate the effect of a single subcutaneous injection of vitamin E and selenium administered immediately before ovsynch on conception rates, antioxidant and plasma progesterone levels of lactating dairy cows. Twenty four healthy cows were randomly distributed into the experimental group (group E, n=14) or the control group (group C, n=10) and synchronized with the ovsynch protocol. In group E, cows received a single subcutaneous injection of 8 mL Esegal (60 mg/mL vitamin E and 1 mg/mL sodium selenite) immediately before ovsynch. In group C, cows did not receive any injection. Blood samples were taken immediately before application and on day 14 after artificial insemination (AI). Pregnancy detection was performed on day 60 after AI. There were no significant differences in conception rates between the groups. The mean erythrocyte GSH-Px and SOD activities in group E on day 14 after AI were higher than group C and their own activities prior to application. The progesterone levels increased in group E compared to group C on day 14 after AI. In conclusion, a single subcutaneous injection of vitamin E and selenium immediately before ovsynch had no a significant effect on conception rates of lactating dairy cows. However, this application had a beneficial effect on erythrocyte GSH-Px and SOD activities and plasma progesterone levels.