Ursodeoxycholic acid is a chemical agent of natural bile acid which is isolated from the bile of bear. It is the stereo-isomer of chenodeoxycholic acid. It has a similar litholysis effect, efficacy as chenodeoxycholic acid. However, it has a short course of treatment and a small dose. It is bound with taurine in the bile in vivo, and is a hydrophilic bile acids as well as a dissolving agent of cholesterol. It can reduce the secretion of cholesterol in the liver, lower the saturation content of cholesterol in bile, promote the secretion of bile acids, and increase the solubility of cholesterol in the bile so that cholesterol gallstones can be dissolved or prevented. Moreover, it can increase the secretion amount of bile, and have a choleretic effect by relaxing the bile duct mouth sphincter which smoothen the discharge of calculus. This product, however, cannot dissolve other types of gallstones.