AS LONG as we know, little attention has been given to evaluating roles of ZnO nanoparticles (ZnONPs) in plants grown under salinity stress. In the present study, biochemical and molecular responses of salt-stressed soybean cv. Giza111 under different ZnONPs were assessed. Treatment with a high NaCl concentration (250mM) alone caused a significant reduction (65%) in germination percentage as well as a significant decrease in all measured growth parameters (root length, shoot height, fresh and dry weight of roots and shoots) and photosynthetic performance (Fv/Fm) compared to control plants. In contrast, malondialdehyde (MDA) & proline contents, and activities of antioxidant enzymes (catalase CAT, peroxidase POX and superoxide dismutase SOD) were highly increased. In contrast, presoaking of soybean seeds with different concentrations of ZnONPs (25, 50, 100, 200mg/L) stimulated the growth of stressed plants which was exhibited by improved growth parameters and photosynthetic performance as well as lower levels of proline and MDA in stressed plants particularly at ZnONPs concentration of 50 mg/L compared to controls. Moreover, isozyme analysis of CAT, POX and SOD showed variable pattern of alleles at 50mg/L ZnONPs. Accordingly, these results recommend application of 50mg/L ZnONPs for improving the productivity of soybean cultivated in saline soils.