Comparison of the effect of American College of Rheumatology 20% improvement criteria (ACR-20) and ACR 50% improvement criteria (ACR-50) between two groups at 12 and 24 weeks. Response rates for ACR-20 and ACR-50 were assessed at 12 and 24 weeks. With an intention-to-treat analysis, response rates for ACR-20 were 30.51% in the chicken type II collagen (CCII) group and 44.94% in the methotrexate (MTX) group at 12 weeks. Response rates for ACR-50 were 8.81% and 15.03%, respectively. Response rates for ACR-20 were 41.55% in the CCII group and 57.86% in the MTX group at 24 weeks. Response rates for ACR-50 were 16.89% and 30.82%, respectively. Both response rates for ACR-20 and ACR-50 of the CCII group were lower than those of the MTX group. These changes were different to a statistically significant degree between the two treatment groups. *P < 0.05 versus CCII group.