In order to investigate the effect of Magnesium nanoparticle spraying solution on some morphophysiological traits of sunflower under experimental drought conditions as split split plot in a randomized completely block design in three replicates at the field of oilseed section of seed and plant Improvement , during 2017-2019 growing season. The treatments including Drought stress at two levels: Normal irrigation and drought stress, Sunflower cultivars studied including: Farrokh, Shams , Qasem & Barzegar, and Magnesium nanoparticles application time at Three Levels: No spraying solution, Spraying at Flowering stage and Grain Filling stage. The results showed that drought stress reduced the amount of traits including: height, shoot dry weight, number of grains per head, 1000 grain weight, head diameter, grain yield, oil percentage and oil yield but Magnesium nanoparticle spraying solution improved the drought stress effect and increased morphological traits. Drought stress increased electrolyte leakage index and decreased relative water content of leaves by 13 and 9 percent, respectively. But magnesium nanoparticles decreased the content of electrolyte leakage index by 9 percent and increased relative leaf water content by10 percent. The response of cultivars to stress levels was not the same and in general, Barzegar, Shams, Qasem and Farrokh cultivars showed the highest tolerance to drought stress, that way, the highest grain yield and oil percentage being related to Barzegar cultivar by 3427.53 kg/h and 43.96 percent, respectively.