<i>Background:</i> Osteoporosis, a major health problem among postmenopausal women, is influenced by dietary factors. The purpose of the present study was to evaluate the hypothesis that erythrocyte levels of n–3 polyunsaturated fatty acid (PUFA) and the dietary intake of fish are associated with risk of osteoporosis and correlate with bone mass in postmenopausal Korean women with the disease. <i>Methods:</i> Fifty cases and 100 controls were recruited. Osteoporosis was defined according to the International Society for Clinical Densitometry guideline as a score lower than –2.5 SD below the T-score for lumbar vertebrae L₁–L₄, femoral neck or femoral total. <i>Results:</i> The T-score of the femoral neck was positively correlated with erythrocyte levels of n–3 PUFA, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and the intake of fish, and was negatively correlated with the ratio of n–6/n–3 PUFA after adjusting for age, years after menopause and height. In addition, the risk of osteoporosis was positively associated with erythrocyte levels of saturated fatty acids but negatively associated with EPA + DHA. <i>Conclusions:</i> Erythrocyte levels of n–3 PUFA and the intake of fish were positively correlated with bone mass. In particular, erythrocyte levels of EPA + DHA reduced the risk of osteoporosis in postmenopausal Korean women.