PURPOSE: To obtain a composition having excellent vulcanization characteristics, processability, etc. and giving an excellent vulcanized product in high rate of cure, by compounding a specific fluorine-containing elastomer copolymer with a tertiary phosphine, an organic halide, a polyhydroxyl compound and a bivalent metal (hydr)oxide.

CONSTITUTION: The objective composition is obtained by compounding (A) an elastomer copolymer containing vinyl fluoride unit and at least one other fluorine-containing monomer unit (e.g. hexafluoropropene), (B) a tertiary phosphine of formula (R1, R2 and R3 are 1W22C alkyl, R1 and R2 or R1, R2 and R3 may together with P form a ring), (C) an organic halide (e.g. alkyl halide), (D) a polyhydroxyl compound(e.g. polyhydroxyl aromatic compound) and (E) a bivalent metal oxide, a bivalent metal hydroxide, or their mixture. The amounts of the components B, C, D and E are preferably 0.1W0.8, 0.05W1.0, 0.6W2.0 and 2W 6pts.wt. per 100pts.wt. of the component A, respectively.