Serum osteoprotegerin (OPG) level is a key biomarker for numerous traits of clinical importance like diabetes, coronary artery disease, blood pressure, lipid profile, and cancers, but its genetic basis remains poorly understood. We estimated the heritability (h(2)) of serum OPG level in 1442 southern Chinese subjects from 306 families. The h(2) for unadjusted OPG was 0.62 for females and 0.17 for males; and for age-adjusted OPG, 0.75 for females and 0.37 for males. Adjustment for lifestyle factors including calcium and phytoestrogen intake, exercise, smoking, and alcohol consumption exerted only a modest effect on the h(2). In conclusion, we confirmed that circulating OPG is a heritable trait and there is a significant difference in heritability between sexes.