A multilayer ceramic substrate includes a plurality of stacked glass ceramic layers and internal conductors. The glass ceramic layers contain at least one diffusion element selected from the group consisting of Ti, Zr and Mn. The internal conductors contain Ag as a conductive material. The multilayer ceramic substrate is produced by the steps of adding at least one diffusion element selected from the group consisting of Ti, Zr and Mn to conductive paste and diffusing the diffusion element in the glass ceramic layers around the conductive paste. As a result, defects otherwise possibly generated around the internal conductors can be eliminated with exactitude.