Bilirubin (BR) alleviates osteoarthritis (OA) by activating the Nrf2/HO-1 pathway and suppressing NF-κB signaling. This study demonstrates that BR protects chondrocytes from oxidative stress and inflammation, which are key factors in OA progression. In vitro experiments showed that BR treatment reduced oxidative stress and apoptosis in chondrocytes exposed to hydrogen peroxide (H₂O₂), and it also inhibited inflammatory responses in LPS-stimulated macrophages. BR activated the Nrf2/HO-1 pathway, which enhanced antioxidant defenses and reduced the expression of pro-inflammatory cytokines. Additionally, BR suppressed NF-κB signaling, which is involved in inflammation and cartilage degradation. In vivo, BR treatment in an ACLT-induced OA model reduced cartilage degeneration and delayed OA progression, as evidenced by improved cartilage structure and reduced inflammation. BR also increased the expression of type II collagen and decreased the levels of matrix metalloproteinase-9 (MMP-9), indicating its protective effect on cartilage. These findings suggest that BR has therapeutic potential for OA by mitigating oxidative stress and inflammation, making it a promising candidate for OA treatment.Bilirubin (BR) alleviates osteoarthritis (OA) by activating the Nrf2/HO-1 pathway and suppressing NF-κB signaling. This study demonstrates that BR protects chondrocytes from oxidative stress and inflammation, which are key factors in OA progression. In vitro experiments showed that BR treatment reduced oxidative stress and apoptosis in chondrocytes exposed to hydrogen peroxide (H₂O₂), and it also inhibited inflammatory responses in LPS-stimulated macrophages. BR activated the Nrf2/HO-1 pathway, which enhanced antioxidant defenses and reduced the expression of pro-inflammatory cytokines. Additionally, BR suppressed NF-κB signaling, which is involved in inflammation and cartilage degradation. In vivo, BR treatment in an ACLT-induced OA model reduced cartilage degeneration and delayed OA progression, as evidenced by improved cartilage structure and reduced inflammation. BR also increased the expression of type II collagen and decreased the levels of matrix metalloproteinase-9 (MMP-9), indicating its protective effect on cartilage. These findings suggest that BR has therapeutic potential for OA by mitigating oxidative stress and inflammation, making it a promising candidate for OA treatment.