Compounds which are able to reduce damaging effects of various stresses such as drought could be of great importance. In this research, arginine was used as a precursor of nitric oxide or polyamines and the effect of this compound on alleviation of oxidative damages under drought stress has been investigated. Experimental treatments included arginine at three levels (0, 10 and 20 µmol) and, drought stress (induced by polyethylene glycol 6000) at the levels of 0, 13.5% and 17% (W/V). This experiment was conducted as a completely randomized design in a factorial arrangement with three replications. The application of arginine through the root medium, increased drought tolerance of ajwain (Trachyspermum ammi) seedlings. Arginine profoundly induced the activities of phenylalanine ammonia-lyase and, polyphenol oxidase in plants which led to reduction in electrolyte leakage and increasing in relative water content, photosynthetic pigments (chlorophyll a, b, total chlorophyll and, carotenoids), polyphenol compounds, flavonoids, anthocyanin content and, soluble sugar content. It is concluded that the application of arginine appeared to induce pre-adaptive responses to drought stress, leading to promote protective reactions.