Study summary: The present population-based case–control study was designed to examine the effects of iron and various fats on the risk of breast cancer. While dietary fats have been studied extensively in relation to the risk of breast cancer, iron has received little attention. Iron is an essential micronutrient, however it acts as a pro-oxidant and specific fats may augment its less desirable properties. Participants, including 3,452 breast cancer cases and 3,474 age- and frequency-matched controls, underwent person-to-person interviews, completing a detailed food-frequency questionnaire. Iron and fat intakes were estimated based on dietary data and food composition tables. Unconditional logistic regression models were used to calculate the independent and interactive effects of different forms of iron and fats on the risk of breast cancer. Animal-derived (largely heme) iron intake was found to be positively associated with breast cancer risk (odds ration (OR) = 1.49 in the highest vs. lowest quartile of iron intake, 95% confidence interval [CI] 1.25–1.78; P trend < 0.01) after adjustment for known risk factors, as well as antioxidant vitamin intake, isoflavone intake, and vitamin supplement use. The impact of animal-derived iron was found to be comparable in pre- and postmenopausal women. Intake of animal-derived fats was also associated with increased risk (adjusted OR = 1.34, 95% CI 1.14–1.58), especially after menopause. In addition, a significant interaction between iron and fat from animal sources was observed (P < 0.01). The authors conclude that high intake of animal-derived iron may be associated with an increased risk of primary breast cancer in Chinese women. Furthermore, saturated and mono-unsaturated fats also derived from animal sources may augment this effect.