Two field experiments were carried out at an agricultural extension field, El-Mahalla El-Kobra City, Gharbiua Governorate, Egypt during the two successive winter seasons of 2015/16 and 2016/17. The objective of this work was to study the effect of foliar application of zinc-oxide nanoparticles on some physiological characters and yield components as well as quality attributes of four flax cultivars under different irrigation treatments. Three irrigation treatments were applied through three separated irrigation experiments each season (irrigate only life irrigation (IT1), irrigate one irrigation after life irrigation (IT2) and Irrigate two irrigations after life irrigation (IT3). Each irrigation experiment was carried out using a split-plot design with three replications. The four cultivars were plotted in the main plots (Sakha 3, Sakha 5, Giza 11 and Giza 12). However, nano-zinc oxide treatments (control, Nano-ZnO1 (50 ppm) and Nano-ZnO2 (100 ppm) were arranged in the sub-plots. Irrigation treatment (IT3) had superiority and ranked the first for all straw yield traits, no. of capsules per plant, seed and oil yields per hectare, fiber length and fiber yield per hectare. However, irrigation treatment (IT2) recorded the highest total fiber percentage. On contrast, there was no significant variation among the three irrigation treatments for oil percentage trait. The data showed that, Sakha 3 gave the highest values for plant height, technical stem length, fiber length, fiber fineness, total fiber percentage and fiber yield per hectare, while, Giza 11 and Giza 12 recorded the highest values of main stem diameter and straw yield per hectare. Besides, Sakha 5 scored the highest number of capsules per plant, seed and oil yields per hectare and oil percentage. One irrigation treatment (IT1) gave the lowest concentrations of chlorophyll a and b, while, the highest levels of proline, CAT and POX were recorded. With respect to nano –zinc oxide application, foliar spray of Zinc oxide nanoparticles induced a significant increment in all straw, oil and fiber traits except fiber fineness. Application of the highest concentration of zinc-oxide NPs (100 mg/Litre) recorded the highest values of the previous mentioned traits.