IL-23, which is mainly secreted by antigen-presenting cells, is a member of the IL-12 family, which includes IL-12, IL-27, and IL-35. IL-23 is a heterodimeric cytokine, comprised of a unique p19 subunit and p4 subunit, the latter of which is shared with IL-12. The receptor for IL-23 consists of IL-23R and IL-12Rβ1, the latter of which is also characteristic of IL-12. IL-23 is essential for Th17 differentiation, expansion, and survival by binding to its receptor, thereby activating the signaling pathway. Many studies revealed that the IL-23/Th17 pathway is implicated in the pathophysiology of various autoimmune diseases, such as autoimmune arthritis, primary biliary cirrhosis, and inflammatory bowel disease.