It is intended to provide a combination drug for preventing and/or treating an autoimmune disease. More specifically speaking, a combination drug for preventing and/or treating an autoimmune disease which contains a CaMKII inhibitor and a disease-modifying antirheumatic drug; a medicinal composition, a commercial package, a kit, etc. for the combination; an enhancer for the effect of preventing and/or treating an autoimmune disease of a disease-modifying antirheumatic drug which contains a CaMKII inhibitor as the active ingredient; a method of screening a CaMKII inhibitor appropriately usable in combination, and so on.