Ursodeoxycholic acid is an endogenous secondary bile acid produced by bacterial metabolism of bile acids in the intestines. Ursodeoxycholic acid decreases cholesterol absorption, dissolves gallstones, and treats cirrhosis and other liver diseases. This compound exhibits immunosuppressive, antioxidative, hepatoprotective, anticancer, and gastrointestinal motility modulating activities. In animal models, ursodeoxycholic acid decreases spleenocyte proliferation and levels of IL-2, L-6, and IFN-γ, increases levels of IL-10, and prevents allograft rejection. In other animal models, this compound increases levels of glutathione and decreases levels of malondialdehyde, myeloperoxidase, and ROS. In colon cancer cells, ursodeoxycholic acid inhibits cellular proliferation and induces apoptosis; similarly, it also induces differentiation, senescence, and HDAC6-dependent hypoacetylation. In other cancer models, this compound inhibits telomerase and may exhibit chemopreventive potential. In vivo, ursodeoxycholic acid decreases gastrointestinal transit time and increases gastric emptying rates.