Canine Interleukin-1 Receptor Antagonist (IL-1Ra) is an anti-inflammatory cytokine produced by monocytes, macrophages, neutrophils, and other immune cells in dogs (Canis lupus familiaris) that serves as a natural regulator of IL-1–mediated inflammation. IL-1Ra competitively binds to the IL-1 receptor type 1 (IL-1R1) without activating downstream signaling, thereby blocking the pro-inflammatory effects of IL-1α and IL-1β and limiting activation of NF-κB and MAPK pathways that drive fever, leukocyte recruitment, and tissue inflammation. In canine health, IL-1Ra plays an important role in modulating inflammatory conditions such as osteoarthritis, immune-mediated polyarthritis, atopic dermatitis, inflammatory bowel disease, sepsis, and other inflammatory or infectious diseases where excessive IL-1 signaling contributes to pathology. In joint disease specifically, IL-1Ra helps counteract IL-1β–driven cartilage degradation and synovial inflammation, making it relevant to therapeutic strategies including biologic and regenerative medicine approaches. As both a biomarker of anti-inflammatory regulation and a therapeutic target, canine IL-1Ra is important in veterinary medicine for monitoring inflammatory balance and evaluating treatment efficacy. In translational research, dogs serve as valuable spontaneous models for human osteoarthritis, autoimmune disorders, and inflammatory diseases, and characterization of canine IL-1Ra supports studies of cytokine network regulation, resolution of inflammation, and development of targeted immunomodulatory therapies relevant to both canine and human health.