Abstract: A ceramic coating-forming agent of an Mg-M.sup.3+ -O based two-component oxide solid solution capable of forming a ceramic coating excellent in heat resistance, adhesion to a substrate metal, electric insulation and the properties of low thermal expansion, at a low temperature, the agent containing an Mg-M.sup.3+ -O based two-component oxide solid solution of the formula (1),(Mg.sub.1-x M.sup.2+.sub.x).sub.1-y M.sup.3+.sub.y O (1)wherein M.sup.2+ is at least one divalent metal selected from the group consisting of Ca.sup.2+, Mn.sup.2+, Fe.sup.2+, Co.sup.2+, Ni.sup.2+, Cu.sup.2+ and Zn.sup.2+, M.sup.3+ is at least one trivalent metal selected from the group consisting of Al.sup.3+, Mn.sup.3+, Fe.sup.3+, Co.sup.3+, Ni.sup.3+, Ti.sup.3+, Bi.sup.3+ and Cr.sup.3+, x is a number in the range of 0.ltoreq.x<0.5 and y is a number in the range of 0<y<0.5, or an anionic oxide-dispersed Mg-M.sup.3+ -O based two-component oxide solid solution of the formula (2),(Mg.sub.1-x M.sup.2+.sub.x).sub.1-y M.sup.3+.sub.