An object of the present invention is to provide a novel marker for rheumatoid arthritis (RA), and more specifically, to provide a marker whose expression may be specifically increased or decreased in RA. Another object of the present invention is to confirm whether or not miRNA serving as the marker is involved as the etiology of RA, and to provide an inspection method for RA and a therapeutic agent for RA each using the miRNA involved. The marker includes miRNA (for example, miR124a) whose expression is specifically increased or decreased in RA synovial cells based on a small RNA expression profile in the RA synovial cells. In addition, the therapeutic agent for RA includes miRNA (for example, miR124a) as an active ingredient.
