Abstract: Pigment gallstone is one kind of cholelithiasis.Up to now,the mechanism of the formation of pigment gallstones is not clear,and it can not be cured completely.The pigment gallstone is composed of calcium bilirubinate,with a small amount of insoluble inorganic salts such as calcium carbonate.The aim of this paper was to examine the association of calcium carbonate with unconjugated bilirubin using FTIR spectroscopy.The results indicated that solid calcium carbonate can associate with unconjugated bilirubin in aqueous solution to form calcium bilirubinate complex.Addition of bile salts can prevent the association of calcium carbonate with unconjugated bilirubin.A possible formation mechanism of pigment gallstones was discussed.

Key words: Calcium carbonate, Bilirubin, Bile Salts, FT-IR spectroscopy