AbstractFatty acid composition of triglycerides (TGs) and phospholipids (PLs) in breast adipose tissue was analyzed in 73 female breast cancer patients and 55 patients with benign breast disease. No differences were observed in the dietary intake of the major fatty acids (i.e., palmitic, stearic, oleic, and linoleic acids) or in the proportion of TGs and PLs in breast adipose tissue between the two groups. In postmenopausal women, however, the dietary intake ofeicosapentaenoic acid (20: 5n‐3) and docosahexaenoic acid (22: 6n‐3) was significantly lower in the breast cancer patients than in patients with benign breast disease. Accordingly, the percentage of docosahexaenoic acid of PLs in breast adipose tissue was significantly lower in breast cancer patients than in patients with benign breast disease among postmenopausal women. The stage of the breast cancer did not contribute to the observed alterations of fatty acid composition of PLs. Consonant with the previous epidemiologic data, the present results suggest that intake of the long‐chain n‐3 fatty acids (mainly derived from fish) may have a protective effect against breast cancer, particularly in postmenopausal women.