Abstract: Background and Objective: Oregano herb has various pharmaceutical properties. Soil Moisture (SM) deficit has harmful effects on aromatic plants. So, the aim of this study was to decrease the harmful effect of SM deficit on oregano plants by adapting them through the use of glutamic acid (GLU). Materials and Methods: Oregano plants were divided into two main groups. The first group was subjected to different levels of SM: 100, 75, 50 and 25% corresponding to the Field Water Capacity (FWC), while second group was subjected to the same SM levels but GLU was added at 0.3 g L–1 as foliar spray. Fresh Mass (FM), Dry Mass (DM), Volatile Oil (VO) percentage and milliliter 100 plant–1, constituents of VO and proline (PRO) were identified. Results: The SM with GLU treatments increased the FM and DM of herb, VO and constituents of VO and PRO contents compared with the treatments of SM without GLU. Greatest FM, DM and VO were obtained with the treatment of 75% SM×GLU. The values were 59.2, 73.9, 23.8 and 29.8 g plant–1 and 7 and 9 mL 100 plant–1 of both seasons. The maximum values of PRO were resulted under the treatment of 25% SM×GLU with the values of 2.3 and 2.7 μmol g–1. The highest amounts of major components (carvacrol, p-cymene and γ-terpinene) were recorded with the treatments of 25% SM×GLU with the values of 42.9, 24.1 and 17.6%. About 25 and 50% of SM×GLU treatments resulted in the highest values of monoterpene hydrocarbons, MCH (47.5%) and oxygenated monoterpenes, MCHO (47.1%) while 75% of MS without GLU treatment produced the highest amounts of sesquiterpene hydrocarbons, SCH (6.2%) and oxygenated sesquiterpenes, SCHO (5.4%). Conclusion: It can use GLU to decrease the harmful effect of SM deficits.