Objectives: This study aimed to determine the effect of bariatric surgery-induced weight loss on bone marrow adipose tissue (BMAT) and bone mineral density (BMD) in postmenopausal, nondiabetic women. Methods: A total of 14 postmenopausal, nondiabetic women with obesity who were scheduled for laparoscopic Roux-en-Y gastric bypass surgery (RYGB) were included in this study. Vertebral bone marrow fat signal fraction was determined by quantitative chemical shift magnetic resonance imaging, and vertebral volumetric BMD (vBMD) was determined by quantitative computed tomography before surgery and 3 and 12 months after surgery. Data were analyzed by linear mixed model. Results: Body weight [mean (SD)] decreased after surgery from 108 (13) kg at baseline to 89 (12) kg at 3 months and 74 (11) kg at 12 months (P < 0.001). BMAT decreased after surgery from 51% (8%) at baseline to 50% (8%) at 3 months and 46% (7%) at 12 months (P = 0.004). vBMD decreased after surgery from 101 (26) mg/cm 3 at baseline to 94 (28) mg/cm 3 at 3 months (P = 0.003) and 94 (28) mg/cm 3 at 12 months (P = 0.035). Changes in BMAT and vBMD were not correlated (ρ = −0.10 and P = 0.75). Calcium and vitamin D concentrations did not change after surgery. Conclusions: RYGB decreases both BMAT (after 12 months) and vBMD (both after 3 months and 12 months) in postmenopausal, nondiabetic women. Changes in BMAT and vBMD were not correlated. These findings suggest that BMAT does not contribute to bone loss following RYGB.