Although weight, lean mass, fat mass and muscular strength are often found to be intercorrelated, the respective role of each parameter in bone mineral density (BMD) remains unknown in older women. The aim of the present study was to investigate the relationship between body weight and composition and quadriceps strength on femoral neck and lumbar spine BMD in healthy postmenopausal women. The relationship between isokinetic quadriceps strength measured by Biodex and BMD measured by dual energy X-ray absorptiometry was studied in 56 women aged 60–81 (70.5 ± 6.2) years in multiple regression models adjusted for age, body composition and menopausal treatment. Weight and age were associated with femoral neck BMD (33 and 10% of variance accounted for, respectively) and lumbar spine BMD (23 and 8% of its variance). When body weight and quadriceps strength were excluded from the model, lean mass and age were associated with femoral neck BMD (29 and 14% of variance explained, respectively) and lumbar spine BMD (28 and 11% of variance explained, respectively). When quadriceps strength was entered into the model, it was strongly associated with femoral neck BMD (30% of variance accounted for), in addition to lean mass (9%) and age (7%), whereas it was not associated with lumbar spine BMD. In conclusion, lean mass explains a great part of the strong association between body weight and femoral neck and lumbar spine BMD. Quadriceps strength explains a great part of the association between lean mass and BMD at the femoral neck site but not at the lumbar spine site. These results suggest a site-specific effect of muscular strength on bone and a potential role of the age-related decline of muscle strength in age-related bone loss in postmenopausal women.