Rheumatoid cachexia (muscle wasting) in rheumatoid arthritis (RA) patients contributes to substantial reductions in strength and impaired physical function. The objective of this randomised control trial was to investigate the effectiveness of oral creatine (Cr) supplementation in increasing lean mass and improving strength and physical function in RA patients. Method. In a double-blind design, 40 RA patients, were randomised to either 12 weeks supplementation of Cr or placebo. Body composition (dual energy x-ray absorptiometry, DXA, and bioelectrical impedance spectroscopy, BIS), strength and objectively-assessed physical function were measured at: baseline, day 6, week 12 and week 24. Data analysis was performed by ANCOVA. Results. Creatine supplementation increased appendicular lean mass (ALM; a surrogate measure of muscle mass) by 0.52 (± 0.13) kg (P = 0.004 versus placebo), and total LM by 0.60 (± 0.37) kg (P = 0.158). The change in LM concurred with the gain in intracellular water (0.64 ± 0.22 L, P = 0.035) measured by BIS. Despite increasing ALM, Cr supplementation, relative to placebo, failed to improve isometric knee extensor (P = 0.408), handgrip strength (P = 0.833), or objectively-assessed physical function (P's = 0.335 – 0.764). Conclusion. In patients with RA, creatine supplementation increased muscle mass, but not strength or objective physical function. No treatment-related adverse effects were reported suggesting that Cr supplementation may offer a safe and acceptable adjunct treatment for attenuating muscle loss; this treatment may be beneficial for patients suffering from severe rheumatoid cachexia