Study of antioxidant activity (AOA) of essential oils of aromatic plants is an important task for cosmetic chemistry, aromatherapy, food and perfume industry. Usually for creating the compositions in these sectors the researchers use a mixture of two or more oils, rather than the individual ones. In this case, the effects of synergism and antagonism can occur. Previously when studying mixtures of oils from clove and lemon we found a synergistic effect, which was expressed in the increase of AOA of this mixture compared with the corresponding value for the individual oils, and in the study of the mixture of oils from lemon and coriander – antagonism, leading to a sharp decrease in AOA. However, our data on AOA of essential oil mixtures were obtained by one and a sufficiently high concentration of oils in the solution. The aim of this work is to study the dependence of AOA of essential oil mixtures on their concentration in the system and to evaluate the concentration dependence of the synergism and antagonism effects in mixtures of oils. By capillary gas-liquid chromatography dependence of antioxidant activity of mixtures of essential oils from lemon (Citrus limon), coriander (Coriandrum sativum L.) and clove buds (Caryophyllus aromaticus L.), as well as synergism and antagonism oils on the concentration of their mixtures in solution was investigated. Evaluation of antioxidant properties of oil mixtures has been studied using an aldehyde/carboxylic acid assay. Trans-2-hexenal was selected to serve as the test substance. It was found that with decreasing concentration of oil mixtures in the solution, despite the difference in character of these effects, the manifestation of synergism and antagonism became less pronounced. Antagonism oils of lemon and coriander largely offset by the addition of clove oil with high antioxidant activity. The role of strong and weak antioxidants in the oil composition was revealed in synergism and antagonism of their mixtures, which gave the opportunity to clarify the mechanism of these phenomena.