Objective:Rheumatoid arthritis and age are associated with high sarcopenia risk. Exercise is an effective treatment for preventing muscle mass loss in older adult populations. It remains unclear whether exercise affects muscle mass in people with rheumatoid arthritis. Thus, this meta-analysis investigated the effect of exercise on muscle mass gain in patients with rheumatoid arthritis.Data sources:PubMed, EMBASE, the Cochrane Library, the Physiotherapy Evidence Database (PEDro), the China Knowledge Resource Integrated Database, and Google Scholar were systematically searched until June 2021.Methods:The present study was conducted according to the guidelines recommended by the Preferred Reporting Items for Systematic Reviews and Meta-Analysis. Randomized controlled trials (RCTs) that reported the effects of exercise on muscle mass for rheumatoid arthritis were identified. The included RCTs were subject to meta-analysis and risk of bias assessment. Subgroup and random-effects meta-regression analyses were performed to identify any heterogeneity (<i>I</i><sup>2</sup>) of treatment effects across studies.Results:We included nine RCTs with a median PEDro score of 6/10 (range: 4/10–8/10). The weighted mean effect size for muscle mass was 0.77 (95% CI: 0.30–1.24; <i>P</i> = 0.001; <i>I</i><sup>2</sup> = 77%). Meta-regression analyses indicated that the disease duration significantly explained variance of treatment effects across studies (β = −0.006, <i>R</i><sup>2</sup> = 69.7%, <i>P</i> = 0.005).Conclusions:Exercise therapy effectively increased muscle mass in patients with rheumatoid arthritis. Treatment effects may be attenuated in those who have had rheumatoid arthritis for a relatively long time.