Two pot trials were carried out during the 2006 and 2007 seasons to investigate the impact of water stress treatments (80, 60, and 40% available soil moisture) and/or nitrogen fertilizer levels (0, 0.6, 0.9 and 1.2 g N pot -1 as ammonium sulphate) on the fresh mass of herb and essential oil of oregano plants. Supplying plants with a water level of 80% available soil moisture and with 1.2 g N pot -1 were effective in raising the productivity of herb and the content and yield of essential oil. The interaction between these two treatments gave the best results. Concerning essential oil constituents, carvacrol was the major compound, followed by p-cymene, -terpinene was the third component.