In rheumatoid arthritis in human or collagen induced arthritis model in animal, joint inflammation and cartilage destruction are mainly mediated by autoantibodies directed to various self antigens. Type II collagen (CII)–specific antibodies are most likely to play a role in this process and have been shown to induce experimental arthritis in susceptible animals. A seires of important epitopes have been found from CII and also the corresponding antibodies have been also established. The purpose of this study was to reveal how arthritogenic autoantibodies recognize native CII in its triple-helical conformation x ray crystallization techinique followed by molecular dynamics simulation.