The present invention relates to use of peptides as a therapeutic agent, wherein it has been confirmed that the peptides of the present invention significantly inhibit the activity of T cells and the differentiation of T helper 17 cells (Th17 cells), which are associated with autoimmune disease, reduce the secretion of inflammatory cytokine IL-6, and have remarkable effects of treating and improving arthritis in an animal model of arthritis. Therefore, the peptides may be used as an active ingredient in therapeutic agents for various autoimmune diseases such as bone disease, inflammatory disease or rheumatoid arthritis.