IL-1Ra, also known as IL-1F3, is a member of the interleukin 1 cytokine family. It is a receptor antagonist of IL-1, can competitively bind with IL-1R1 thereby blocking cell activation by the cytokine. IL-1Ra is secreted by various types of cells including immune cells, epithelial cells, and adipocytes, and is a natural inhibitor of the pro-inflammatory effect of IL1β. This protein inhibits the activities of interleukin 1, alpha (IL1A) and interleukin 1, beta (IL1B), and modulates a variety of interleukin 1 related immune and inflammatory responses, particularly in the acute phase of infection and inflammation. As a potent immune/inflammatory molecule, IL-1Ra is tightly associated with osteomyelitis, rheumatoid arthritis, traumatic brain injury (TBI) and stroke. Recently, an increasing number of studies proved that IL-1Ra is also actively involved in tumor progression, such as high expression IL-1Ra increased the risk of bladder cancer and non-cardia gastric carcinoma.