This study investigates the potential therapeutic effects of bilirubin (BR) on osteoarthritis (OA) and the underlying mechanisms. OA is a chronic degenerative joint disease characterized by cartilage degeneration and inflammation. Oxidative stress plays a crucial role in the progression of OA, and BR, an endogenous antioxidant, has been shown to scavenge reactive oxygen species (ROS) and exhibit anti-inflammatory properties. The study found that BR protected chondrocytes from hydrogen peroxide-induced oxidative stress by activating the Nrf2/HO-1 pathway and suppressing the NF-κB signaling pathway. In vitro, BR treatment reduced intracellular ROS levels, increased Nrf2 nuclear translocation, and upregulated HO-1 and GPx4 expression. Additionally, BR reduced apoptosis in chondrocytes and decreased the production of pro-inflammatory cytokines in LPS-stimulated macrophages. In vivo, BR significantly reduced cartilage degeneration and delayed OA progression in an ACLT-induced OA model, showing superior efficacy compared to hyaluronic acid (HA). These findings suggest that BR has a protective effect on chondrocytes and can delay OA progression caused by oxidative stress.This study investigates the potential therapeutic effects of bilirubin (BR) on osteoarthritis (OA) and the underlying mechanisms. OA is a chronic degenerative joint disease characterized by cartilage degeneration and inflammation. Oxidative stress plays a crucial role in the progression of OA, and BR, an endogenous antioxidant, has been shown to scavenge reactive oxygen species (ROS) and exhibit anti-inflammatory properties. The study found that BR protected chondrocytes from hydrogen peroxide-induced oxidative stress by activating the Nrf2/HO-1 pathway and suppressing the NF-κB signaling pathway. In vitro, BR treatment reduced intracellular ROS levels, increased Nrf2 nuclear translocation, and upregulated HO-1 and GPx4 expression. Additionally, BR reduced apoptosis in chondrocytes and decreased the production of pro-inflammatory cytokines in LPS-stimulated macrophages. In vivo, BR significantly reduced cartilage degeneration and delayed OA progression in an ACLT-induced OA model, showing superior efficacy compared to hyaluronic acid (HA). These findings suggest that BR has a protective effect on chondrocytes and can delay OA progression caused by oxidative stress.