The present disclosure relates to a prepreg formed by drying a fabric substrate impregnated with a resin composition by means of heating until the resin composition is in a semi-cured state. The resin composition contains (A) at least one of an epoxy resin having naphthalene skeleton and a phenolic curing agent; and (B) a polymer having structures represented by the following formulae (I) and (II), no unsaturated bond between carbon atoms, an epoxy value ranging from 0.2 to 0.8 ep/kg, and an weight-average molecular weight ranging from 200,000 to 850,000: wherein X:Y=0:1 to 0.35:0.65, R1 represents H or CH3, and R2 represents H or an alkyl group.