Abstract Plant responses to oxidative injuries and content of antioxidants were comparatively studied in five soybean cultivars (L 17 , Clean, T.M.S, Williams×Chippewa and M 9 ) at the three levels of irrigation. In order to measure the water deficit stress, the irrigation was applied based on three levels of evaporation from the 'class A' pan (50 mm; optimum condition of irrigation, 100 mm; moderate water deficit and 150 mm; extreme water deficit). A two-year field experiment was conducted in 2008 and 2009. The experimental design was a split plot in a randomized complete block design with four replications. The output results showed that, water deficit stress significantly increased activities of some antioxidant enzymes (catalase and glutathione redoctase) as well as ABA and Proline content. Lipid and protein oxidation (malondialdehyde and dityrosine contents) also increased significantly at the moderate and extreme water deficit stress. The relative water content, seed and oil yield were affected by water deficit and were reduced by both levels of water deficit. Among cultivars, L 17 and Williams×Chippewa produced the highest seed and oil yield at the optimum condition of irrigation and both levels of water deficit stress, respectively. Assessment of correlation results indicated that, there was a positive and significant correlation among activity of antioxidant enzymes, ABA and proline content with seed and oil yield in both levels of water deficit stress, as well
