A sintering temperature can be lowered to 1,200.degree. C. by adding from 15% by weight or more to 35% by weight or less of rutile-type titanium dioxide into forsterite. By carrying out sintering at such a low temperature, a sintered product can be obtained in which sintering was carried out while retaining the respective crystal phases of the forsterite and rutile-type titanium dioxide. Such a sintered product is an excellent high-frequency ceramic composition, wherein the high quality factor Qf value derived from forsterite is hardly impaired, and, the absolute value of the temperature coefficient .tau..sub.f is controlled to 30 ppm/.degree. C. or less by rutile-type titanium dioxide.