Phytoestrogens are naturally occurring compounds found most commonly in legumes and soy products. Because of their structural similarities to that of estrogen, the effects of dietary phytoestrogens has been largely studied to understand possible correlations between phytoestrogen intake and estradiol levels in women. Though the mechanism has not fully been confirmed, it is often hypothesized that functional phytoestrogens, or isoflavones (e.g. genistein and daidzein), have the ability to weakly bind to estrogen receptors and can act as either estrogen receptor agonists or antagonists. Previous research on this topic remains inconclusive in terms of determining whether this estrogen receptor binding action leads to an increase or decrease in serum estradiol levels. This remains particularly relevant as increased estradiol levels are often associated with higher risks of breast cancer, osteoporosis, and cardiovascular disease in women. Due to inconsistencies in previous findings, a cross sectional analysis was performed to investigate the relationship between dietary isoflavone intake and serum estradiol levels. This analysis was run using a dataset from the Study of Women’s Health Across the Nation (SWAN), a multi-site and multi-ethnic cohort of women aged 42-52 years old at baseline. Isoflavone intake levels were derived via a food frequency questionnaire obtained from an interview. The database had also been recently updated to better estimate isoflavone intake by improving the assessment of isoflavone content in listed foods. The participants were separated into tertiles based on increasing levels of isoflavone intake. Because the average dietary isoflavone levels were extremely low in White, Black and Hispanic participants ( <2.39mg), these groups were ultimately excluded from the study and the analyses were confined to that of Chinese (average isoflavone intake=16.29mg) and Japanese participants (average isoflavone intake= 18.8mg). In addition, we excluded those with extreme dietary values ( too many or too few solid foods/day, more than 10 foods skipped, and daily caloric intake too high or too low). Separate linear regression models were conducted for both the Chinese and Japanese combined group and ethnic-specific samples. Tertiles of the isoflavones intake was modeled. Menopausal status, age, BMI, day of menstrual cycle, total energy intake, dietary fat intake, dietary fiber intake, physical activity, smoking and alcohol consumption were examined as potential covariates to be included in the final model. The fully adjusted model included BMI, age, menstrual status, and day of menstrual cycle, as these covariates were statistically significant when run with dietary isoflavone intake levels. Mean age for the combined Chinese and Japanese group was 46.1 with mean BMI of 23.1. In the combined group, 61% of participants were in the premenopausal state with 39% in early peri-menopausal state. There was not any significant associations found in both combined and ethnic specific models. Because this newly updated dataset did not prompt any significant results, other sex hormones should be included to assess if they are influenced by isoflavone intake. Sex hormone binding globulin could potentially play a role in isoflavone binding and estradiol levels and thus should be further explored in follow up analysis.