Limited and inconsistent studies exist on the association between the intake of fish, n-3 polyunsaturated fatty acids (PUFA), and n-6 PUFA and breast cancer. Fish and n-3 PUFA support various body functions and are thought to reduce the carcinogenesis risk while n-6 PUFA may have a positive association with cancer risk. We examined the association between intake of fish, n-3 PUFA (including eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), docosapentaenoic acid (DPA), alpha linolenic acid (ALA)), and n-6 PUFA and breast cancer with sub-analyses on estrogen (ER) and progesterone receptor (PR) status. We investigated 38,234 Japanese women aged 45-74 years from the Japan Public Health Center-based prospective Study (JPHC), and during 14.1 years of follow-up time, 556 breast cancer cases were newly diagnosed. Breast cancer risk was not associated with the intake of total fish, n-3 PUFA, and n-6 PUFA when analyzed in totality through multivariable Cox proportional hazards regression models with age as the time-scale. Intake of total n-6 was positively associated with the development of ER+PR+ tumors [multivariable adjusted HR Q4 vs Q1 =2.94 (95% CI: 1.26-6.89; ptrend =0.02)]. Intake of EPA was associated with a decreased breast cancer risk for ER+PR+ tumors [multivariable adjusted HR Q2 vs Q1 =0.47 (95% CI: 0.25-0.89; ptrend =0.47)]. While the overall association between the intake of total fish, n-3 PUFA, and n-6 PUFA and breast cancer risk is null, for ER+PR+ tumors, a positive association was seen between n-6 intake and breast cancer, and a marginally significant inverse association was observed for EPA intake. This article is protected by copyright. All rights reserved.