To identify the predictive role of pretreatment skeletal muscle mass index (SMI) for long-term survival of bladder cancer patients. Several databases were searched for studies investigating the relationship between pretreatment SMI and prognosis in bladder cancer. The overall survival (OS) and cancer-specific survival (CSS) were defined as primary and secondary outcomes, respectively. Hazard ratios (HRs) and 95% confidence intervals (CIs) were combined. Nine studies involving 1476 cases were included. The results demonstrated that a lower pretreatment SMI was significantly related to poorer OS (HR = 1.56, 95% CI: 1.33-1.82, P<0.001) and subgroup analysis based on thresholds of SMI revealed similar results. Besides, pretreatment SMI was also obviously related to CSS (HR = 1.75, 95% CI: 1.36-2.25, P<0.001). Lower pretreatment SMI was associated with worse long-term survival of bladder cancer patients.