INTRODUCTION: In the present study, we investigated the effects of breast-feeding time on bone mineral density (BMD) later in life. MATERIAL AND METHODS: The current study was based on a retrospective analysis of 586 postmenopausal women with a mean age of 60.8 years, who were screened for osteoporosis by dual energy X-ray absorptiometry (DXA).They were classified into 4 groups with respect to the duration of their breast-feeding as never (group 1), 1-24 months (group 2), 25-60 months (group 3), or > 60 months (group 4). Bone mineral density results for the femur neck and lumbar spine were classified into 3 groups according to WHO criteria as normal (T score > -1.0 SD), osteopenia (T score -1.0 to -2.5 SD), and osteoporosis (T score < -2.5 SD). Patients with osteopenia or osteoporosis (T score < -1.0 SD) were considered as having low bone mass (LBM). RESULTS: We found a correlation between duration of lactation and femur BMD or spine BMD in the study population (r = 0.116, p < 0.005; r = -0.151, p = 0.001, respectively). Significant differences were found between femur BMD and spine BMD of groups in one-way ANOVA analysis (p = 0.025, p = 0.005, respectively). Additionally, when compared with the other three groups, group 4 was older and had longer duration of menopause (p < 0.01). In logistic regression analysis, age and body mass index were found as independent risk factors of LBM [odds ratio: 1.084 (95% CI 1.031-1.141); odds ratio: 0.896 (95% CI 0.859-0.935)], while duration of lactation was not found as an independent predictor of LBM. CONCLUSIONS: In this study, we have found that changes of bone metabolism during lactation had no effect on postmenopausal BMD measured by DXA. Consequently, it can be suggested that long breast-feeding duration is not a risk factor for low bone mass later in life.