The effect of the mixture of two antioxidants has been evaluated on the thermal‐oxidant degradation of the hydroxyl‐terminated polybutadiene (HTPB) because of its importance in the coatings and adhesives industries. 2,2‐Methylene bis(4‐methyl‐6‐tertiarybutylphenol) or A.O.2246 and 3‐hydroxy pyridine have been considered as antioxidants in this study as a common HTPB antioxidant and an active antioxidant, respectively. The thermal‐oxidant degradation behavior of the HTPB has been investigated in the presence of a mixture of two antioxidants by TGA and DTG tests, and, subsequently, the results of these tests have been interpreted by two model‐free methods, e.g., Kissinger–Akahira–Sunose and Friedman methods. The results revealed that the mixture of two antioxidants affected the activation energy of the thermal‐oxidant degradation reaction of the HTPB. The calculated activation energy value obtained from the Kissinger–Akahira–Sunose method was about 199 ± 1 kJ⋅mol−1. In addition, the Ea value at various conversion rates has also been calculated by using the Friedman method. This method showed that the highest Ea value in the thermal‐oxidant degradation reaction belonged to the initiation step of the reaction (about 299 kJ⋅mol−1). Moreover, the lowest activation energy value was correlated to the second step of the degradation reaction at a conversion rate of 0.6 (about 184 kJ⋅mol−1).