The frequency of black stones was found to be 8.6% (37/430) in our department. Twenty-five black stones were studied by scanning electron microscopy, x-ray microanalysis and neutron activating analysis. The gross appearance of black stones was black or dark brown in color and coralline or round in shape. The cut surface was irregular with an amorphous structure and rare lamination. The ultrastructure of the core were divided into 4 types: Type I: flat and smooth with irregular space in 7 stones (28%); Type Ⅱ: flat and composed of numerous granules about 30-50 nm. in diameter in 8 stones (32%), Type Ⅲ: irregular and amorphous structure, with ball-like particles in 3 stones (12%); and type Ⅳ: other irregular structures of thin plates or small particles in 7 stones (28%). The concentration in calcium of black stones was 29.53±7.62% of the total weight and those stones were radiopaque. The metal elements of Type I weremainly Cu and Fe, in addition to Ca. In the Type Ⅱ, Hg, S and Ca could be detected. The elements in the ball-like particle of Type Ⅲ were mainly P and Ca. The thin plates of Type Ⅳ were probably calcium phosphate and the irregular particle were calcium bilirubinate. The structure of the black stone was much more amorphous than that of other gallstones. The Ca, Cu and Fe were main metal elements. The component of calcium bilirubin could be found in about one third of the black stones in the central portion. Because the final residue of black stones was very abundant, further investigation is needed in the future.