Rheumatoid arthritis is a chronic autoimmune disease characterized by an elevated synovial inflammatory response, with destruction or erosion of articular cartilage in major joints. The aim of the present study was to examine whether 20‑hydroxyecdysone (HES) is able to ameliorate oxidative stress and inflammatory responses in a collagen‑induced rheumatoid arthritis (CIA) rat model. A total of 40 healthy male rats were selected arbitrarily and separated into four groups. Rats treated with saline served as a control (group I), rats subjected to CIA induction by intradermal injection of bovine collagen II type served as the induced group (group II), while rats induced with CIA and administered with 10 and 20 mg/kg bodyweight HES for 28 days served as treatment groups (groups III and IV). Biochemical parameters, including paw swelling (edema), arthritis score, indexes of thymus and spleen, antioxidant levels (superoxide dismutase, catalase and glutathione), articular elastase and anti‑collagen II specific immunoglobulins (Ig)G, IgG1 and IgG2a, in addition to inflammatory markers [nitric oxide, C‑reactive protein, interleukin (IL)‑1β, IL‑6, tumor necrosis factor‑α and nuclear factor‑κB p65 subunit] were significantly decreased (P<0.01) following supplementation with HES (10/20 mg/kg). Consistently, the protein expression pattern of inducible nitric oxide synthase and cyclooxygenease‑2 were significantly downregulated (P<0.01) upon treatment with HES. In addition, histological analysis confirmed arthritis in CIA‑induced rats by revealing the presence of greater polymorphonuclear cell infiltration, with eroded articular cartilage and prominent synovitis. However, administration of HES was demonstrated to alleviate the morphological changes and maintain the normal architecture of synovial joints. In conclusion, the results of the present study indicated that treatment with HES (particularly 20 mg/kg) may effectively eradicate the inflammatory cascade and oxidative stress process in CIA‑induced rats and thereby exhibit anti‑rheumatoid arthritis properties.