This research was carried out to study the effect of TiO2 and nano-TiO2 on some chemical compounds in a medicinal plant Lallemantia iberica under water deficit conditions. The experiment was conducted as a factorial arrangement in a randomized complete block design with three replications. The first factor was the application of external materials as spraying with 3 levels of control, TiO2 and nano-TiO2, and the second factor was 100% (no stress), 75% (moderate stress) and 35% (severe stress) irrigation content. The results of measurements showed moderate stress and the use of nano-TiO2 caused a significant increase in phenolic content, total flavonoid and antioxidant activity; severe drought stress significantly reducing these compounds. The effect of nano-TiO2 on catalase and superoxide dismutase enzyme activity was also significant, and in the treatment of nano-TiO2 and moderate stress, the highest activity level of these two enzymes was observed. Identification of phenolic compounds of the extracts by HPLC indicated the production of vanillic, ferulic acid and syringic acid by nano-TiO2 spray application. Gallic acid was measurable in moderate and severe stress and caffeic acid in severe stress under the influence of nTiO2. The sinapic acid and syringic acid contents increased under moderate stress and severe stress decreased them. Finally, it is concluded that nano-TiO2 in comparison with TiO2 reduces the effects of drought stress on L. iberica and can be used to produce this plant in water-deficit areas. Manuscript profile