To obtain a thermosetting resin compsn. suitable for producing a cast ceramic composite sheet by compounding a polyvinyl butyral resin or/and a poly(meth)acrylic resin, a specific maleimide compd., a cross-linker, a cure catalyst, and a solvent.

This compsn. is prepd. by compounding 100 pts.wt. maleimde compd. represented by the formula (wherein X and Y are each H, methyl, or ethyl), 10-100 pts.wt. resin comprising a polyvinyl butyral resin or/and a poly(meth)acrylic resin, 30-150 pts.wt. cross-linker, a cure catalyst, and a solvent (e.g. toluene, a ketone, or an alcohol) which can homogeneously dissolve the foregoing ingredients. The compsn. can be homogeneously mixed with a ceramic powder (e.g. silica) to give a mixture, which can be easily cast on a release sheet and, when dried, gives a sheet with enough strengths and a nonsticky surface. The sheet can be easily cured by heating, giving a ceramic composite molding suitable for electronic and electric parts.