To homogeneously sinter a large-scaled ceramic compact by scattering reaction-preventing powder such as alumina, beryllia, magnesia or zirconia on a waste plate formed with the same materials as an object to be burnt and subjected to cleaning, and then by burning the object to be burnt in a mounted state on the plate.

The method comprises: (1) subjecting a waste plate 4 pressure- formed with materials for a ceramic resonator to cleaning at ca. 900°C for 5 h.; (2) scattering zirconia powder, having ca. 50 μm average particle diameter, as a reaction-preventing powder 3 so as to be about 3 mm thick on the inside bottom of a burning sheath 2; (3) placing the waste plate 4 on the powder layer and then scattering zirconia powder as a reaction-preventing powder 3 so as to be about 15 mm thick; (4) putting a ceramic resonator element as an object 1 to be burnt on them and subjecting it to cleaning at ca. 900°C for 5 h., followed by sintering it in a retained state at ca. 1,350°C for 5 h. Thus, an excellent sintered compact free from uneven burnt portion in its exterior too is produced without deformation and a crack.