PURPOSE: A fibrous base material is impregnated with a phenolic resin having a specific curing rate and dried by heating, thus producing prepregs suitably used for laminates because of its good electrical and physical properties at a high speed.

CONSTITUTION: A phenol such as cresol is made to react with an aldehyde such as paraformaldehyde in the presence of an alkali catalyst such as monomethylamine to prepare a phenolic resin composition with a curing time of 30W180sec at 150°C and a viscosity of 10 poise at 25°C. After the resin composition is diluted with a diluent such as water or alcohol, a fibrous base material such as paper or glass cloth is impregnated therewith at 25W40°C and dried by heating to product the objective prepreg.