A novel method is proposed to quantify carvacrol in oregano oil and nanocapsules containing oregano oil by means of gas chromatography coupled to mass spectrometry. This is a fast, simple, and efficient method (with average analyte recoveries between 95 and 100%) capable of identifying, quantifying and validating all compounds that made up oregano essential oil, free and nanocapsulated. Chromatographic conditions were also optimized: an RTX-5MS column was employed, helium was the carrier gas at a flow rate of 0.99 mL / min and a temperature program was included, allowing the separation of the baseline from both compounds in less than 31 minutes. The method showed satisfactory sensitivity, specificity, linearity, precision, accuracy, limit of detection and limit of quantification for analyzes of carvacrol in oregano oil and in the nanocapsules containing the oil. The main compounds identified in oregano essential oil were carvacrol (78.82%), p-cymene (10.45%), γ-terpinene (5.69%), linalool (1.47%) and thymol (1.23%) were detected as the other major compounds. The proposed method is suitable for a reliable separation, identification and quantification of the present compound (carvacrol) in essential oil of oregano and nanocapsules containing the essential oil. It can be proposed as an analytical method for the analysis of carvacrol and after formulations that have incorporated it into their edible formulations.