Drought stress affects the morphology, physiology, and biochemistry of plants and will have major effects on agricultural production. This study was conducted to evaluate the effect of drought on some physiological and grain yield properties of Balangu populations (Lallemantia royleana Benth. ), in the Research Station of Shahed University. This study was conducted in a split-plot design based on randomized complete block design (RCBD) with three replications during 2014-2015. The experimental factors consisted of three different levels of drought stress at the flowering stage as main factors (applying soil water potential of-0. 5,-6. 5 and-9. 5 atm), and Balangu populations including one population from Kurdistan and four populations from Esfahan province (Esfahan3, Esfahan5, Esfahan6, Esfahann) were considered as subplots. The traits studied included grain yield, one thousand seed weight, photosynthetic pigments content, proline content, total phenol content, membrane stability index (MDA), and peroxidase activity. According to the results, drought stress had significant effects on all traits except chlorophyll b content and chlorophyll a/b ratio. Population and its interactions showed a significant effect with all traits except anthocyanin content. Drought caused to the reduced content of photosynthetic pigments, membrane stability index, thousand grain weight and grain yield. With increasing drought stress, the lipid peroxidation enzymatic activity and non-enzymatic antioxidants such as phenolic content, carotenoids content, anthocyanins content, and proline content of tissue increased to induce drought tolerance. The highest grain yield with the mean of (312. 77 kg/ha) and the highest phenolic content with an average of (14. 02 mg/g FW) were recorded for the Esfahan3 population under relatively severe stress.