Abstract: Extreme hot weather is occurring more frequently due to global warming, posing a significant threat to species survival. Birds in particular are more likely to overheat in hot weather because they have a higher body temperature. This study used a heat stress model to investigate the antioxidant defense mechanisms and changes in fatty acid catabolism in Red-billed Leiothrix (Leiothrix lutea) to gain an understanding of how birds adapt to high temperatures. The birds were divided into five groups: a control group (30 ℃ for 0 days), 1 D group (40 ℃ for 1 day), 3 D group (40 ℃ for 3 days), 14 D group (40 ℃ for 14 days) and recovery group (40 ℃ for 14 days, then 30 ℃ for 14 days). Our results indicated that when Red-billed Leiothrix are subjected to heat stress, malondialdehyde (MDA) content in the liver significantly increased, as did the enzyme activities of catalase (CAT), glutathione–SH–peroxidase (GSH-PX) and total antioxidant capacity (T-AOC) in the liver. Furthermore, there was a significant increase in heat shock protein 70 (HSP₇₀) expression in the liver, while avian uncoupling protein (avUCP) expression in muscle was significantly reduced. Additionally, there was a significant reduction in fatty acid catabolism enzyme activity such as 3-hydroxyacyl-CoAdehydrogenase (HOAD) activity in the heart, and carnitine palmitoyl transferase 1 (CPT-1) and citrate synthase (CS) activity in the heart and liver. Furthermore, fatty acid translocase (FAT/CD₃₆) in the heart, heart-type fatty acid binding protein (H-FABP) and fatty acid binding protein (FABP-pm) in the liver and heart were also significantly decreased. These changes reverted after treatment, but not to the same level as the control group. Our results indicated that when Red-billed Leiothrix are exposed to heat stress their internal antioxidant defense system is activated to counteract the damage caused by high temperatures. However, even with high antioxidant levels, prolonged high temperature exposure still caused some degree of oxidative damage possibly requiring a longer recovery time. Additionally, Red-billed Leiothrix may be able to resist heat stress by reducing fatty acid transport and catabolism.