Objective: To investigate the difference in the effect of non–weight-bearing body fat mass on bone mineral density between premenopausal and postmenopausal women. Methods: We studied 252 regularly menstruating premenopausal women and 213 postmenopausal women with right side dominance. Age, years since menopause (in postmenopausal women), height, weight, and body mass index were recorded. Bone mineral density of non–weight-bearing sites (ie, arms), weight-bearing sites (ie, lumbar spine including L2–4 and legs), and body fat mass were measured by whole-body scanning with dual-energy x-ray absorptiometry. Body fat mass was also measured by dual energy x-ray absorptiometry. Results: Body fat mass did not differ between groups. In postmenopausal women, body fat mass correlated positively with bone mineral density of the left leg (r = .41, P < .001), right leg (r = .36, P < .001), left arm (r = .31, P < .001), and lumbar spine (r = .27, P < .001). The correlation between body fat mass and bone mineral density of the left arm remained significant after adjusting for age, years since menopause, and height. In premenopausal women, body fat mass correlated positively with bone mineral density of left leg (r = .37, P < .001) and right leg (r = 0.31, P < .001), but correlated weakly with bilateral arms (r ≤ .19) and lumbar spine bone mineral density (r = 0.13, P < .05). Conclusion: The effect of non–weight-bearing body fat on bone mineral density was greater in postmenopausal than premenopausal women.