Oregano (Origanum vulgare L.) is an aromatic plant very rich in essential oil which in turn is an important natural resource of thymol and carvacrol. These compounds can be transformed to more valuable thymoquinone. Herein, a comparative study is presented explaining the oregano essential oil oxidation applying potassium monopersulphate or hydrogen peroxide catalyzed by two different so-called biomimetic catalysts: Fe (III) meso-etraphenylporphyrin or Fe (III) phthalocyanine. Both are highly efficient catalysts in the process of the KHSO5 oxidation of essential oil. A complete substrate conversion was observed within 1h and the cocatalyst ammonium acetate did not influence the catalytic process. When H2O2 was used as oxidant, a relatively slower conversion and lower reaction yield were observed and the presence of ammonium acetate affected the oxidation cycle with both catalysts. In conclusion, the essential oil rich in thymol (47.6%) and carvacrol (25.1%) can be easily oxidized to oil containing thymoquinone (19.1-63.3%) as the main or as one of the main components.