Background: Causes of weight change after tocilizumab treatment are unclear. We aimed to investigate the effects of tocilizumab treatment on body weight and serum adipokine levels in patients with rheumatoid arthritis (RA). Methods: In this retrospective cohort study, we evaluated weight changes in patients with RA who received methotrexate (Cohort I) or tocilizumab with methotrexate (Cohorts II and III) for 24 weeks. Adipokine concentrations at baseline and 24 weeks were analyzed in Cohorts I and III. Cohorts I and II received tocilizumab therapy for an additional 48 weeks, during which weight changes were monitored (24–72 weeks). Results: No significant weight change occurred after 24 weeks of methotrexate treatment (mean difference, −0.2 kg; P = 0.630), but was observed after 24 weeks of tocilizumab treatment (mean difference, +0.9 kg; P = 0.010). Weight changed regardless of the treatment response in both treatment groups. The leptin–adiponectin ratio (P = 0.015) and levels of adiponectin (P < 0.001), leptin (P < 0.001), and resistin (P = 0.003) increased significantly after 24 weeks of tocilizumab, but not methotrexate treatment. After 24, 48 and 72 weeks of tocilizumab treatment in Cohort II, mean (95% confidence interval [CI]) weight changes from baseline were +0.7 (0.0–1.4), +1.2 (0.4–2.0) and +1.1 (0.2–2.0) kg, respectively, and mean (95% CI) percent weight changes from baseline were +1.3% (0.1%–2.6%), +2.2% (0.7%–3.6%), and +2.0% (0.4%–3.7%) at 24, 48, and 72 weeks, respectively. Conclusion Weight and the leptin–adiponectin ratio increased after tocilizumab treatment. Given that cardiovascular (CV) risk factors may deteriorate in patients with RA who receive tocilizumab, further studies are required to determine the effects of weight gain on CV outcomes in these patients.