We aimed to assess if exercise applied after bariatric surgery (BS) improves bone mineral density (BMD) compared to usual care. Systematic search was conducted up to January 2021. Effect measures were determined using standardized mean difference (SMD) with 95% confidence interval (CI). Certainty evidence was assessed according to GRADE. Four clinical trials encompassing 340 patients were included. Exercise induced a positive BMD effect at total hip (SMD = 0.37 [95% CI 0.02, 0.71]; very low certainty evidence), femoral neck (SMD = 0.63 [95% CI 0.19, 1.06]; low certainty evidence), lumbar spine (SMD = 0.41 [95% CI 0.19, 0.62]; low certainty evidence), and 1/3 radius (SMD = 0.58 [95% CI 0.19, 0.97]; low certainty evidence). Exercise undertaken after BS seems to induce a positive effect on BMD.