Analysis of different extracts of Satureja hortensis L. obtained with various solvents (by supercritical CO 2 and by traditional extraction techniques) is presented in this study to identify and to determine the major constituents responsible for the antioxidant activity. The total polyphenol and total flavonoid contents of the extracts were determined by spectrophotometric method and no correlation was found with the antioxidant activites. HPLC was also used to measure two diterpenes as carnosol and carnosic acid in the extracts. Neither carnosol nor carnosic acid were identified. Individual antioxidants as rosmarinic and caffeic acids were identified and quantified with TLC-densitometry method. Rosmarinic acid was found in higher amount than caffeic acid. The content of rosmarinic acid was also determined with HPLC. A good correlation coefficient of 0.85 was found between the antioxidant activity and amount of rosmarinic acid, which leads to the conclusion that rosmarinic acid is among the main antioxidant compounds of S. hortensis L. plant.