Disclosed is a fluoroelastomer that, while maintaining cold resistance possessed by cold-resistant fluororubbers, has low hardness and very low permeability to a fuel. Also disclosed are a composition for peroxide vulcanization and an automotive component in a fuel system that has been molded using the composition. The fluoroelastomer is a peroxide vulcanizable fluoroelastomer. The fluoroelastomer is a block copolymer consisting of a fluoroelastomer segment (A) having either (1) a vinylidene fluoride/perfluoroalkyl vinyl ether copolymer composition ratio of 50 to 85/15 to 50% by mole or (2) a vinylidene fluoride/tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer composition ratio of 45 to 85/1 to 30/15 to 30% by mole, and a fluoroelastomer segment (B) substantially incompatible with the fluoroelastomer segment (A) and contains an iodine atom.
