Approximately 40,000 women in the U.S. are diagnosed with endometrial cancer annually. Biological data suggest coffee or tea consumption may lower endometrial cancer risk through estrogenic and insulin-mediated pathways. Epidemiologic data are inconsistent, with two of three prospective cohort studies showing an inverse association with coffee consumption and two prospective cohort studies finding no association with tea consumption. We used publicly available data from the Women's Health Initiative Observational Study to evaluate the association between coffee, tea and endometrial cancer risk. We identified 48,912 eligible post-menopausal women with a mean follow-up time of 7.5 years. During this period there were 452 incident endometrial cancer cases. We used Cox-proportional hazard models to evaluate the effects of coffee and tea consumption on endometrial cancer risk, while adjusting for potential confounders including age, body mass index and hormone therapy use. Overall, we did not find an association between coffee consumption and endometrial cancer risk. Compared to women who did not drink coffee on a daily basis (none or < 1 cup/day), the multivariable adjusted hazard ratios for women who drank 2-3 cups/day was 0.95 [95% confidence interval (CI) 0.74,1.22] for total coffee, 0.91 (95% CI 0.68,1.23) for regular coffee, and 0.94 (0.62,1.42) for decaf coffee. Compared to obese women who did not drink coffee on a daily basis (none or < 1 cup/day), the multivariable adjusted hazard ratios (HR) for obese women who drank ≥ 2cups/day as reported at baseline were: 0.79 (95% CI 0.53,1.17] for total coffee, 0.62 (95% CI 0.39,1.00) for regular coffee, and 0.78 (95% CI 0.40,1.50) for decaf coffee. Furthermore, obese women who consistently reported drinking ≥2 cups of regular coffee/day had an even further reduced risk [HR 0.40 (95% CI 0.18,0.91)]. In comparison to women who did not drink tea on a daily basis, obese women who drank 1 cup and ≥ 2cups of tea/day had multivariable adjusted hazard ratios of 0.45 (95% CI 0.22,0.92) and 0.99 (95% CI 0.60,1.62), respectively. The results from our study suggest that regular coffee consumption may be protective against endometrial cancer among obese postmenopausal women, with inconclusive results for tea. Our study adds to the biological understanding and to the small body of prevalent epidemiologic literature on coffee consumption and endometrial cancer risk.