The correlation between the efficacy of type II collagen (C II) treatment of the rheumatoid arthritis (RA) and the existence of HLA-DRB 1 * 0405 allele was investigated in two groups of patients; the first group had HLA-DRB 1 * 0405 allele (the 0405 group) and the second had no such allele (the non-0405 group). Thirty-eight RA patients were given a chicken cartilage soup containing heat degenerated C II (the CII group) or a placebo soup (the placebo group) for three months. The 38 cases were composed of 11 cases in the 0405/C II group, 9 in the 0405/placebo group, 11 in the non-0405/C II group, 9 cases in the non-0405/placebo group. In the C II group, there was a significant increase in the anti-human C II IgA antibody serum titers (p = 0.003) and significant decrease in the anti-human C II IgG titer (p < 0.0001). The differences in the number of swollen and tender joints were statistically significant between the 045/C II and 0405/placebo groups (p of the swollen joints = 0.03, and p of the tender joints = 0.03), and between the 0405/C II and non-0405/C II groups (p = 0.006 and 0.01, respectively). We concluded that oral C II could have a therapeutic efficacy in RA patients with HLA-DRB 1 * 0405 allele.