A cured or uncured composition of homo- or copolymer of epihalohydrins comprising a homo- or copolymer of an epihalohydrin, curable amounts of a curing agent therefor and an acid acceptor, characterized in that said curing agent and acid acceptor consist, on the basis of 100 parts by weight of said homo- or copolymer of epihalohydrin, of (a) 0.1 - 10 parts by weight of a cyclic carboxylic acid anhydride, (b) 0.1 - 10 parts by weight of a compound selected from the group consisting of 1,8-diazabicyclo(5,4,0)undecene-7 and salts thereof, and (c) 0.5 - 20 parts by weight of a metal compound selected from the group consisting of the oxides of the metals of group II of the periodic table of elements, hydroxides of said group II metals, carbonates of said group II metals, carboxylic acid salts of said group II metals, oxides of the metals of group IVa of the periodic table of elements, basic carbonates of said group IVa metals, basic carboxylic acid salts of said group IVa metals and basic phosphites of said group IVa metals.