Ursodeoxycholic acid (ursodiol or UDCA) is a main active compound of bile bear which has been widely used in traditional Chinese medicine for the purpose of promoting the flow of bile (choleretic effect). It is a secondary bile acid resulting from bacterial actions in the colon, and is normally present as a minor fraction of the total bile acids in humans. However, it alters bile acid composition, resulting in decreases in the concentration of the more hydrophobic and cytotoxic bile acids. Furthermore, some studies have suggested that ursodeoxycholic acid protects hepatocytes against bile acid-induced apoptosis. Recently, ursodeoxycholic acid is increasingly used for the treatment of cholestatic liver diseases.