Abstract: A ceramic trimmer capacitor comprising a cylindrical casing, a stator and a rotor comprising a rotor casing and a dielectric assembly consisting of a disk-shaped ceramic dielectric member, a semicircular dielectric layer formed upon the upper surface of the dielectric member and having a low dielectric constant less than 20 and a coefficient of thermal expansion substantially equal to the dielectric member and a rotor electrode formed on the whole surface of the dielectric member including the semicircular dielectric layer, the dielectric assembly being inserted into the rotor casing and electrically and mechanically connected thereto; the stator and the rotor being placed in the cylindrical casing and resiliently supported. Stray capacitance is almost negligible; the variable capacitance range may be considerably improved; and the mechanical strength may be increased. The ceramic trimmer capacitor is especially adapted to be used in an electronic watch.