Water shortage is one of the most important limiting  factors for  crop production, that affected growth and yield by changing physiological conditions. This study was carried out to investigate effect of oxidative stress on antioxidant defense mechanism in Research greenhouses of Birjand University in 2014. A factorial arrangement of treatments based on randomized complete block design (Due to the lack of uniformity of light) with four replications was used .The studied factors were drought stress with three levels including 100, 75 and 50 percent of plant water requirement (non-stress, moderate and severe stress respectively) and millet genotype with three levels (including Bastan, promising lines KFM5 and KFM20).. Malondialdehyde, electrolyte leakage and membrane stability  was measured in 30 and 45 days after stress and yield in maturity. Antioxidant activity (including SOD, CAT and APX) was measured in 30 days after stress. The results showed that antioxidant activity  increased as  intensity  of drought stress increased in all three genotypes.  Bastan had the highest antioxidant activity  under sever stress that showed it had best antioxidant defense system and better scavenge reactive oxygen species than another genotypes. The malondialdehyde content (MDA)  was low in Bastan compared to other genotypes  and was less affected by increasing drought stress that showed this genotype was less affected by oxidative stress. Seed yield decreased as intensity of drought stress increased in all three genotypes and had negative correlation with antioxidant activity.