A cross-linkable fluoroelastomer remarkably excellent in cross-linkability and a method for its production, a fluoroelastomer composition excellent in the cross-linked physical properties, and a cross-linked rubber. A cross-linkable fluoroelastomer having a Mooney viscosity of from 20 to 300, obtainable by heat-treating a mixture of a fluoroelastomer (A), an organic peroxide (B) and at least one additive (C) selected from the group consisting of a C12-28 higher fatty acid, a metal salt of a C12-28 higher fatty acid, an ester of a C12-28 higher fatty acid, an amide of a C12-28 higher fatty acid and a C12-28 higher aliphatic alcohol, at a temperature of from 110 to 380° C.