G009, isolated from the mycelia of Ganoderma lucidum, has been reported as a potent liver-protecting compound. To characterize this compound, its physicochemical properties were studied. The average molecular weight of the most abundant constituent of G009 was 9.4 kD. The contents of carbohydrate and protein in G009 were 70% and 12.4% respectively. The main carbohydrate constituents were glucose, xylose, mannose and galactose. Seventeen kinds of amino acid were detected. The contents of carbon, hydrogen, and nitrogen were 40, 5.7, and 1.8%, respectively. Ca, Mg, Zn were also determined.