To provide a prepreg for a glass cloth base copper-clad laminate being free of voids and excellent in the precision of plate thickness and a prepreg for a multilayer printed wiring board built up with a glass cloth base being excellent in pattern precision, free from voids and excellent in the precision of plate thickness.

In regard to a thermosetting resin-impregnated prepreg prepared by impregnating glass cloth with thermosetting resin and drying, the surface roughness of the prepreg is made 5 μm or less. Besides, the prepreg prepared by impregnating the glass cloth with the thermosetting resin so that the whole thickness be 1.3-2.0 times as large as the thickness of the glass cloth and by drying is passed in heating and under pressure between a pair of rotating hot rolls. Thereby the prepreg having the surface roughness of 5 μm or less can be obtained economically.