A ceramic valve supporting structure comprising in use for internal combustion engine; a ceramic valve (1) having an integral stem (1b), the upper portion of which is provided with a circular groove (2); a cotter (3) the outer surface of which is tapered, and formed by butting a pair of semi-cylindrical pieces, and having a lock projection (3a) placed into the groove (2) when secured concentrically to the outer surface of the stem, a cylindrical retainer (4) concentrically secured to the cotter surface of the cotter so as to support the valve (1) through the cotter (3); the retainer (4) being provided with the inner surface tapered in a direction so as to make the cotter (3) tightly engage with the outer surface of the stem (1b) by means of wedge effect against the tapered cotter (3) due to the urging force of a coil spring member (6) axially exerted to the retainer (4); and a stress relief means provided so as to avoid the predetermined portion of the cotter from locally engaging against the outer surface of the stem. Stress relief is provided by a bevelled portion (4c) at the end of the retainer (4) adjacent the valve head to provide a clearance between the retainer (4) and cotter (3) at the end of the cotter.