Antioxidant efficiency and chemical constituents of Thymus Pallescens de Noé essential oil were examined. Also, the effect of thermal treatments (100°, 150° and 190°C) for 3 hours on the antioxidant activity and chemical constituents of the oil was studied. Antioxidant activity was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPHâ¢) free-radical scavenging and reducing power, and compared with synthetic antioxidant (butylated hydroxytoluene, BHT) and the oil kept at room temperature. The main compounds were carvacrol (42.9â44.1%), p-cymene (10â11%) and γ-terpinene (7.9â10.5%). The oils being heated did not significantly affect for their chemical composition. The antioxidant activities were dose-dependent and varied with the temperature and the method used.