A process for manufacturing a prepreg exhibiting excellent formability and producing laminated boards and multiple layer circuit boards exhibiting high thickness precision is disclosed. The process of manufacturing the prepreg comprises (a) a step of impregnating a glass fiber substrate with a solvent, (b) a step of impregnating the solvent-impregnated glass fiber substrate with epoxy resin, (c) a step of heating the epoxy resin-impregnated glass fiber substrate, (d) a step of further impregnating the epoxy resin-impregnated glass fiber substrate, in which the epoxy resin has been cured, with the epoxy resin, and (e) a step of heating the lastly obtained epoxy resin-impregnated glass fiber substrate, wherein the epoxy resin reaction rate in the inner layer is 85% or more and the epoxy resin reaction rate in the outer layer is 60% or less.