Drought stress affects a vast range of morphological, physiological and biochemical characteristics in medicinal and aromatic plants. Lippia citriodora has been traditionally used in infusions for the treatment of asthma, cold, fever, spasms, colic, diarrhea and indigestion. This study examined the impacts of various drought stress levels including 10% (WD1), 30% (WD2), 50% (WD3) and 70% (WD4) water depletion of field capacity on essential oil composition of Lippia citriodora under greenhouse conditions. Essential oils were isolated by hydro-distillation procedure and characterized using GC and GC/MS apparatus. Data were subjected to analysis of variance in a completely randomized design with three replications (n=3). The maximum (0.79%) and the minimum (0.43%) essential oil content were obtained under WD4 and WD1 treatments, respectively. The results also showed that essential oil of lemon balm plant predominantly consisted of monoterpenes such as 1,8-cineol, cis-and trans-thujene, camphor, and borneol. According to the results of GC-MS analysis, geranial (27.31 %), neral (19.28 %) and limonene (14.35 %) were the major constituents of essential oil under moderate water stress (WD3). However, the highest content of neral, limonene and geranial were obtained at low drought stress (WD1). Apart from the tremendous negative effects of drought situations on growth and development, the corresponding stress situations frequently lead to an increase in the concentration of natural products. In principle, there are different possibilities to explain this enhancement. First, it could be the consequence of a reduced production of biomass in the stressed plants: when the rate of biosynthesis of natural products is not changed or only slightly reduced, their concentration on dry or fresh weight basis simply will be elevated. Alternatively, the drought stress enhances the actual rate of biosynthesis. This could be due either to a passive shift or an active up-regulation of the en
