The invention relates to flame-retarded compositions comprising A) an epoxy resin mixture consisting of A1) 15-35% by weight of at least one liquid epoxy resin, A2) 55-85% by weight of aluminum oxide trihydrate having a particle size of D.sub.50 20-25 .mu.m as determined by sieving, A3) 0-20% by weight of at least one further filler and A4) 0-5% by weight of at least one conventional additive and B) at least one carboxylic acid anhydride or a cycloaliphatic diamine of the formula I or II ##STR1## in which the radicals R.sub.1 to R.sub.4 independently of one another are hydrogen or C.sub.1 -C.sub.4 alkyl and Z is a direct bond, --CH.sub.2 --, --C(CH.sub.3).sub.2 --, --S--, --O--, --SO.sub.2 -- or --CO--, in an amount sufficient to cure component A, the content of components A2 and A3 together being 63-80% by weight, with respect to the total weight of the composition. These compositions are suitable for use in high voltage components, such as flyback transformers.