The purpose of this research was to determine the effects of different silicon concentrations on the physiological and morphological characteristics of purple basil under drought stress conditions. For this purpose, a factorial experiment based on a completely randomized design with three replications was done. The studied factors were four levels of drought stress (25, 50, 75, and 100% full irrigation) and 3 levels of silicon foliar application (0, 1, and 1.5 mM). Results showed that height, number of leaves, dry weight of shoots, and a, b, and total chlorophyll content of the purple basil had a significant decrease with increasing of drought stress (P<0.01). Using silicon especially at1 mM, the damages of drought stress on purple basil was decreased compared to control. Generally, the results of this research represent the positive role of silicon in decreasing the effects caused by drought stress in studied plant.