Abstract: The use of nanomaterials, especially nanoparticles, in plant physiology is crucial for understanding their effects on plant development and productivity, as well as for assessing potential environmental risks to food safety and human health. Zinc oxide nanoparticles are among the most widely produced, used, and likely to be released into the environment. The study assessed the effects of ZnO nanoparticles on the photosynthetic activity, pigment content, enzymes activity of barley (Hordeum vulgare) plants under normal irrigation and drought conditions. The results showed that the application of ZnO nanoparticles improved the resistance of barley plants to drought stress. This was evidenced by increased chlorophyll pigment and carotenoids levels in the leaves, decreased activity of antioxidant enzymes (CAT, POX and APX) under drought stress, and significant change in the Fv/Fm parameter of chlorophyll fluorescence (ChlaF). In conclusion, our findings suggest that ZnO nanoparticles played a significant role in enhancing the tolerance of plants to drought stress.