Soy isoflavones have been hypothesized to exert hormonal effects and to enhance bone mineral density in postmenopausal women. To test this hypothesis, we studied the effects of soy isoflavones supplements on bone mineral density and sex hormones (serum estradiol, sex hormone-binding globulin and testosterone) in 47 postmenopausal women. There were 24 participants in the treatment group and 23 in the control group. The treatment group consumed the isoftavones extract capsule daily (which contained 90 mg of soy isoflavones) for 12 weeks. The study compared pre- and post-isoflavones intake in the following areas: physical examination, diet survey, bone mineral density and serum sex hormone levels. The average age of the treatment group was 64.63 years and that of the control group was 66.48 years. There were no significant differences between the two groups in terms of height, weight, and body mass index. Both groups maintained regular diet patterns in terms of their average daily nutrient intake. There was no significant difference between the treatment group (18.49 mg) and the control group (21.27 mg) in terms of daily isoflavones intake based on diet. The 12-week analysis of bone mineral density change after taking isoflavones supplements demonstrated no significant differences in the following : lumbar spine BMD (0.82 g/$ extrm{cm}^2$ in pre versus 0.81 g/$ extrm{cm}^2$ in post), femoral neck BMD (0.58 g/$ extrm{cm}^2$ in pre versus 0.57 g/$ extrm{cm}^2$ in post) in the treatment group. There was no significant difference in serum estradiol in the isoflavones treatment group. The subjects indicated no significant difference in serum testosterone in the isoflavones treatment group. But the subjects indicated a significant difference in sex hormone-binding globulin (60.04 nmol/L in pre versus 52.39 nmol/L in post) in the isoflavones treatment group at the levels of p < 0.05. The significant decrease in sex hormone-binding globulin did indicate the need for long-term study on isoflavones supplementation as well as its positive effect on bone mineral density.