OBJECTIVE: The aim of this study was to determine the relationship between dietary total antioxidant capacity (dTAC) and risk of breast cancer among Iranian women. DESIGN: In this hospital-based case-control study, dietary intake of participants was collected using a 168-item validated FFQ. Dietary TAC was assessed using FRAP assay considering. Logistic regression was used to obtain ORs for breast cancer across quartiles of dTAC. SETTING: Cancer Institute, Iran. PARTICIPANTS: We included 412 women with pathologically confirmed breast cancer and 456 apparently healthy controls. RESULTS: Mean dTAC was 11·3 ± 5·8 for cases and 12·1 ± 7·9 for controls. A trend towards significant inverse association was seen between dTAC and odds of breast cancer in the whole population; such that after controlling for several potential confounders, individuals in the highest quartile of dTAC were 0·39 times less likely to have breast cancer than those in the lowest quartile (0·61; 95 % CI: 0·38, 0·99, P < 0·05). In the stratified analysis by menopausal status, we found that postmenopausal women with the greatest dTAC had lower odds for breast cancer, compared with those with the lowest dTAC (0·47; 95 % CI: 0·24, 0·93, P < 0·05). This association strengthened after additional adjustment for BMI (0·28; 95 % CI: 0·11, 0·72, P < 0·05). No significant association was seen between dTAC and odds of breast cancer in premenopausal women. CONCLUSIONS: We found that dietary TAC was inversely associated with risk of breast cancer, in particular among postmenopausal women. Prospective cohort studies are needed to confirm these findings.