OBJECTIVE:Breast-feeding is associated with maternal health, such as electrolyte metabolism, lipid profile and body component change. The aim of this study was to evaluate the relationship between duration of breast-feeding and obesity in postmenopausal women. METHODS:We analyzed data from the Korea National Health and Nutrition Examination Survey (KNHANES) 2010-2012, a cross-sectional study in a Korean population. A total of 6621 postmenopausal women were analyzed. RESULTS:Body mass index and waist circumference were greater in women who had breast-fed for 6 months or more than in those who had not (BMI: 23.7±0.1 vs 24.5±0.1, P<0.0001; WC: 80.6±0.4 vs 82.8±0.3, P<0.001). This association persisted after adjustment for confounding factors (BMI: odds ratio[OR]1.54, 95% confidence interval[CI] 1.19-2.0; WC: OR1.67, 95% CI 1.29-2.17). The duration of breast-feeding tended to increase with increasing BMI and WC (P for trend, 0.001 for each). The proportions of women with greater BMI and WC increased with increasing duration of breast-feeding (27.3% in ≤6 months vs 41.2% in >18months, P<0.0001). CONCLUSION:The results of this study suggest that prolonged breast-feeding may be associated with greater BMI and WC among postmenopausal women.