A multilayer ceramic substrate according to the present invention includes a plurality of base layers that are laminated containing a low-temperature co-fired ceramic material, a plurality of first constraint layers which contain a metal oxide not completely sintered at the sintering temperature of the low-temperature co-fired ceramic material and which are located between the base layers, and a protective layer which contains the metal oxide and which is in contact with an outermost base layer of the plurality of base layers in the lamination direction, and wherein X1>X2, where X1 is a content of the metal oxide in a surface section of the protective layer and X2 is a content of the metal oxide in a boundary section of the protective layer that is in contact with the outermost base layer.