Thymus daenensis Celak. is an endemic medicinal plant in Iran, with high essential oil content and rich source of thymol. In this study effect of water deficit stress (normal irrigation, withholding irrigation in start of flowering and withholding irrigation in vegetative stage) on agro morphological traits, essential oil content and components were investigated. Results indicated that measured agro morphological traits with the exception of leaf and flower weight did not significantly affected by severity of stress. The highest (0.31 g) and the lowest (0.15 g) of leaf and flower weight was observed in normal irrigation and withholding irrigation in start of flowering treatment, respectively. Essential oil content and constituents with the exception of α-thujene did not affected by water deficit stress. The highest of essential oil content (4.7 %) was observed in withholding irrigation in start of flowering treatment. Under all treatments, oxygenated monoterpenes and thymol were the main class of compounds and the major constituent of essential oil, respectively. Thymus daenensis Celak. indicated a good tolerance to water deficit and had a good biomass and essential oil content in these conditions and so can be a suitable choice for culture in arid and semi-arid regions
