Objective:To study the role of some oxidative stress biomarkers in conception during foal heat. Methods:Ultrasound scanning was used to confirm the presence of mature ovulating follicle (>30mm) in mares exhibited foal heat on days7 to9 postpartum.Daily blood samples were collected from parturition till foal heat to measure equine lysozymes, nitric oxide(NO), catalase (CAT), total proteins and globulins.Lipid peroxide(MDA), reduced glutathione(GSH), ascorbic acid(AA) and zinc were measured during foal heat expression form day7 to10 post foaling. Results:Lysozymes were high on days1 and9 postpartum but low level was recorded on day 6.NO, total proteins and globulin peaked on days5 and6 but low level was recorded on day9. HighMDA(P<0.03), zinc(P<0.05) levels were observed on days8 and9.HighGSH was observed on day9.AA(P<0.03) andCAT levels were low on days8 and9.Non conceived mares had high MDA, low zinc,AA,CAT andGSH.Conclusions:Mares during the foal heat are subjected to oxidative stress on days8 and9 as expressed by lowAA, zinc, andGSH and highMDA and mares with sufficient antioxidant capacity can overcome this stress and conceive.Some mares need to be supplied during foal heat with antioxidants to improve their immunity and overcome oxidant/antioxidant imbalance to conceive.This study recommends the use of ascorbic acid and zinc as supplements during foal heat.