Flame retardant epoxy resin compositions

A flame retardant epoxy resin composition comprising

• (A) an epoxy resin having an epoxy equivalent of at least 185 and possessing a skeleton having in its molecular structure at least one structure in which two benzene rings are conjugable to each other directly or via an aliphatic unsaturated double bond, carbon atoms having an atomic orbital of SP.sup.2 type accounting for at least 50% of the total number of carbon atoms in the epoxy resin,
• (B) a phenolic resin having a hydroxyl equivalent of at least 160, carbon atom,, having an atomic orbital of SP.sup.2 type accounting for at least 85% of the total number of carbon atoms in the phenolic resin,
• (C) a polyimide resin having one of the following formulae (2) or (3) as a main constituent unit:
• ##STR37## wherein R.sup.2 is a tetravalent organic group of 6 to 30 carbon atoms containing one or more aromatic rings or aromatic heterocyclic rings, R.sup.3 is a divalent organic group of 6 to 30 carbon atoms containing one or more aromatic rings and/or a divalent organic group which is an aliphatic diamine residue containing a siloxane structure, R.sup.4 is a hydrogen atom or an alkyl group of 1 to 4 carbon atoms, R.sup.5 is a trivalent organic group of 6 to 20 carbon atoms containing one or more aromatic rings or aromatic heterocyclic rings and n is a number such that the polyimide resin has a weight average molecular weight of about 5,000 to about 300,000, in an amount of 1 to 20 parts by weight per 100 parts by weight of the epoxy resin and the phenolic resin combined, and
• (D) at least 70% by volume of the entire composition of an inorganic filler, said composition being substantially free of bromine compounds and antimony compounds.