Rheumatoid arthritis (RA) is an autoimmune disease represented by chronic inflammation and following structural damage at the articular joints. Progression of the disease causes disability and subsequent early retirement or a care-requiring condition. Although new agents have the potential of complete inhibition of joint damage, there is still a considerable number of patients with progressed joint damage who couldn't receive the benefits of these agents because of the long duration of their disease or uncontrollable disease activity. Thus, a new treatment tool for RA aiming at joint repair is necessary. Mesenchymal stem cells (MSCs) are known to build bone and cartilage, and also have immunosuppressive ability. We have considered MSCs as a new treatment tool of RA, and have reported that MSCs suppress osteoclastogenesis. More recently, we also reported that inflammation induces osteogenesis and suppresses the chondrogenesis of MSCs. An investigation of a new delivery system of MSCs to the target lesion is now ongoing. The data from this investigation suggest that MSCs can be a new application in the treatment of RA.