Formation of gallstones depends upon at least 2 processes; first, supersaturation of cholesterol and calcium salts, seond, nucleation of crystals in the bile. Nucleation requires gallbladder mucins, and its main component, glycoprotein, is known to be concentrated in the gallstones. Howere the nature and role of the gallstone proteins is still unknown, and the difference in the compositions of proteins between various gallstones has not been observed. 21 gallstones, 13 cholesterol stones and 8 pigment stones, were obstanined at cholecystectomy, washed, dried and extracted cholesterol, pigment, and bile salts by 0.1 N HCl petrolium ether ethanol solution for an analysis of proteins in gallstones. The compositions of gallstones by infrared sphectophmeter. The gallstone proteins were then quantified by Bensadoun & Weinstein method, and analyzed by SDS-polyacrylamide gel eletrophoresis. The results were as follaws; 1) The amount of gallstones proteins was 2.12 mg% in cholesterol stones and 2.61mg% in pigment stones. 2) SDS-PAGE could isolate low molecular proteins; 13 cases (62%) below 15 KD, 3 cases (14.2%) between 20~40 KD and 5 cases (23.8%) above 45 KD of molecular weight. 3) There was no significant difference in protein quantification between cholesterol and pigment stones. We could suggest that gallstone proteins are mainly acidic proteins with low molecular weight and these proteins could play an important role in nucleation of gallstone formation.