The composition of essential oils depends among others on the characteristics of the starting material and production process. In this work, dried Origanum vulgare L. leaves were subjected to gamma irradiation and then processed by steam distillation to obtain an essential oil, which was analyzed by GC-MS and HPLC-DAD. The composition of the essential oil was determined, and changes in the aromatic profile were analyzed by changes in both chromatographic profile and compound content. Among the aromatic compounds of the oregano essential oil, a significant direct relation with irradiation dose was observed for four compounds (Myrcene, p-cymene, carvacryl methyl ether and l-borneol), whereas important changes were observed for carvacrol and thymol in those irradiated samples when compared with the non-irradiated control sample oil.