To manufacture a prepreg sheet adapted to obtain a laminate having little microvoids by arranging plastic films each having mold releasability on both surfaces of thermoset resin powder paper making sheet, passing the resin between a pair of rolls while melting to heat it, and pressurizing it.

A thermosetting resin powder paper making sheet is obtained by wet paper making a slurry containing fibers of timber fibers of the like and thermosetting resin powder of a phenol resin or the like as main components, and may be blended with a curable binder as needed. The prepreg for an electrically insulating material as for a printed circuit board and the like is manufactured by arranging plastic films each having mold releasability on both surfaces of the thermosetting resin powder sheet, passing the resin between a pair of rolls while heating to melt it, and pressurizing the sheet. The sheet is molded by releasing the plastic films from it immediately before use, then laminating it with other sheet, and molding it by a hot press or the like.