There is few data on the association between dietary fiber intake and estrogen receptor (ER)/progesterone receptor (PR)-defined breast cancer risk. We evaluated the association between dietary fiber and ER/PR-defined breast cancer risk stratified by postmenopausal hormone use, alcohol intake, and family history of breast cancer in the population-based Swedish Mammography Screening Cohort comprising 51,823 postmenopausal women. Fiber intake was measured by food-frequency questionnaire collected in 1987 and 1997. Relative risks (RRs) were estimated by hazard ratio derived from Cox proportional hazard regression models. During an average of 8.3-year follow-up, 1,188 breast cancer cases with known ER/PR status were diagnosed. When comparing the highest to the lowest quintile, we observed non-significant inverse associations between total fiber intake and the risk of all tumor subtypes; the multivariate-adjusted RRs were 0.85 (95% CI: 0.69-1.05) for overall, 0.85 (0.64-1.13) for ER+PR+, 0.83 (0.52-1.31) for ER+PR- and 0.94 (0.49-1.80) for ER-PR-. For specific fiber, we observed statistically significant risk reductions for overall (34%) and for ER+PR+ (38%) for the highest versus lowest quintile of fruit fiber, and non-significant inverse associations for other subtypes of cancer and types of fiber. Among ever-users of postmenopausal hormone (PMH), total fiber intake and especially cereal fiber were statistically significantly associated with approximately 50% reduced risk for overall and ER+PR+ tumors when comparing the highest to the lowest quartile, but no association was observed among PMH never users. Our results suggest that dietary fiber intake from fruit and cereal may play a role in reducing breast cancer risk.