In a sintered body of low temperature cofired ceramic constituting ceramic layers of a multilayer ceramic substrate provided with external conductor films, which is obtained by sintering a non-glass low temperature cofired ceramic material, respective crystalline phases of quartz, alumina, and fresnoite are deposited. The ceramic layers are, because of being in the form of a sintered body of non-glass low temperature cofired ceramic, less likely to fluctuate in composition, and the multilayer ceramic substrate can be thus inexpensively and easily manufactured therefrom. In addition, the ceramic layers have the above-mentioned respective crystalline phases deposited therein, and thus have a high joint strength with the external conductor films, and moreover, the sintered body itself has a high fracture touhgness value.