The present invention provides a millable silicone rubber composition characterized by comprising: (A) two raw alkenylated organopolysiloxane rubbers (A-1) and (A-2), i.e., a raw organopolysiloxane rubber including a molecular chain which is represented by a specific empirical formula and in which each of both terminals has been blocked with a trialkenylsiloxy group and a raw organopolysiloxane rubber including a molecular chain which is represented by a specific empirical formula and in which each of both terminals has been blocked with a monoalkenyldialkylsiloxy group; (B) an organohydrogenpolysiloxane having at least two silicon-atom-bonded hydrogen atoms in the molecule; (C) carbon black having an average primary-particle diameter of 100-350 nm; (D) reinforcing fumed silica having a specific surface area, as determined by the BET adsorption method, of 50 m2/g or greater; and (E) a platinum-group metal catalyst. This millable silicone rubber composition has an excellent electric-field relaxation ability, a high elongation at break, a reduced tension set, and high dielectric or insulating properties.