PURPOSE: To obtain a prepreg resin composition improved in heat, impact and water resistances by mixing a specified aromatic polysulfone with a bisphenol epoxy resin, N,N,N',N'-tetraglycidyldiaminodiphenylmethane and diaminodiphenyl sulfone.

CONSTITUTION: 15-45wt.% aromatic polysulfone comprising at least 50mol% repeating units of formula I and at most 50mol% at least one kind of repeating unite selected from among those of formulas II-XVII and having a reduced viscosity of 0.35-0.6g/dl as measured in dimethylformamide in a concentration of 1g/dl at 30°C is mixed with 5-60wt.% bisphenol epoxy resin and 50-80wt.% N,N,N',N'-tetraglycidyldiaminodiphenylmethane. 0.7-1.3 equivalents (in terms of the amino group), per equivalent of the epoxy groups in the bisphenol epoxy resin, of a diaminodiphenyl sulfone is added to the obtained composition.