The relationship between the thermal behavior and antioxidant stability of rosemary extract (RE) was investigated. Through simultaneous thermal analysis (TG-DTA) and total phenolic content measurement, stability of RE below 200°C and the resistance of phenolics below 130°C have been found, revealing an asynchrony between weight loss and destruction of antioxidant capacity. Peroxide value, p-anisidine value, TG-DTA, Rancimat test, and kinetic analysis of chicken fat at 90-150°C were also carried out to further determine the antioxidant stability of RE on the oxidation and degradation of edible fats. Consequently, the highest antioxidant activity index is 6.49 at 120°C, and RE elevates the initial degradation point of chicken fat under thermal stress by reducing oxygen absorption. Besides, the antioxidant effect of RE is found to be weaker due to the thermal destruction of the phenolics, but a higher temperature below the destruction point can cause a better antioxidant effect. Novelty impact statement:1. The antioxidant effect of RE is related to temperature and the thermal stability of components.