Tensile and dielectric properties of short aramid or carbon fiber reinforced chlorosulfonated polyethylene(CSM) composites were investigated. The composites were prepared by the mill-mixing method. The effects of vulcanization, fiber types and contents on the tensile strength, dielectric loss tangent(tan δ), specific inductive capacity(ε_r), and volume resistivity were discussed. The short fiber reinforced CSM composites showed better tensile and dielectric properties when CSM matrix was vulcanized. Tensile properties of the CSM composites with or without vulcanization were affected by the fiber types and the effect was larger in case of the aramid fiber reinforced composites. The tan δ and ε_r were affected by the fiber types and contents in the unvulcanized CSM composites, whereas those dielectric properties increased with fiber contents regardless of fiber types in the vulcanized CSM composites. It was observed that the volume resistivities of the CSM composites were almost same as that of the CSM matrix regardless of fiber types and contents.