Abstract Context Bone loss after bariatric surgery potentially could be mitigated by exercise. Objective To investigate the role of exercise training (ET) in attenuating bariatric surgery–induced bone loss. Design Randomized, controlled trial. Setting Referral center for bariatric surgery. Patients Seventy women with severe obesity, aged 25 to 55 years, who underwent Roux-en-Y gastric bypass (RYGB). Intervention Supervised, 6-month, ET program after RYGB vs. standard of care (RYGB only). Outcomes Areal bone mineral density (aBMD) was the primary outcome. Bone microarchitecture, bone turnover, and biochemical markers were secondary outcomes. Results Surgery significantly decreased femoral neck, total hip, distal radius, and whole body aBMD (P < 0.001); and increased bone turnover markers, including collagen type I C-telopeptide (CTX), procollagen type I N-propeptide (P1NP), sclerostin, and osteopontin (P < 0.05). Compared with RYGB only, exercise mitigated the percent loss of aBMD at femoral neck [estimated mean difference (EMD), −2.91%; P = 0.007;], total hip (EMD, −2.26%; P = 0.009), distal radius (EMD, −1.87%; P = 0.038), and cortical volumetric bone mineral density at distal radius (EMD, −2.09%; P = 0.024). Exercise also attenuated CTX (EMD, −0.20 ng/mL; P = 0.002), P1NP (EMD, −17.59 ng/mL; P = 0.024), and sclerostin levels (EMD, −610 pg/mL; P = 0.046) in comparison with RYGB. Exercise did not affect biochemical markers (e.g., 25(OH)D, calcium, intact PTH, phosphorus, and magnesium). Conclusion Exercise mitigated bariatric surgery–induced bone loss, possibly through mechanisms involving suppression in bone turnover and sclerostin. Exercise should be incorporated in postsurgery care to preserve bone mass.