To obtain a one-puck type thermosetting resin composition improved in heat resistance and storage stability by using five specified compounds as the essential components.

N,N'-(4-,4'-diaminodiphenylmethane)bismaleimide (A) represented by formula I is mixed with 2,2'-bis[4-(4-maleimidophenoxy)phenyl]propane (B) represented by formula II. The total weight of components A and B should be 30-60wt.% based on the total resin composition in order to attain heat resistance. The mixing ratio between components A and B is such that the ratio A/(A+B) is 20-50. To this mixture, o,o'-diallylbisphenol A is added in an amount to give a C/(A+C+B) of 50-100%, and the obtained mixture is agitated, molten by heating to 130-160°C and cooled to 120°C or below. To this cooled mixture, 10-40wt.%, based on the total resin composition, diallyl isophthalate (D) represented by formula IV is added, and a small amount of a peroxide compound (E) is added to improve the curability of the resin composition to obtain a one-pack type thermosetting resin composition.