A millable silicone rubber composition comprising: an alkenyl group-containing organopolysiloxane gum consisting of components (A-1) and (A-2) below in a total amount of 100 parts by weight (A-1) 10 to 100 parts by weight of an organopolysiloxane gum of average compositional formula below which is capped at both ends of the molecular chain with trialkenylsiloxy groups and has an alkenyl group content of 0.25 mol% or less (wherein each R 1 is a like or unlike alkenyl group of 2 to 8 carbon atoms, each R 2 is a like or unlike group selected from the group consisting of alkyl groups of 1 to 20 carbon atoms and aromatic hydrocarbon groups of 6 to 20 carbon atoms, each R 3 is a like or unlike group selected from R 1 and R 2, the subscript "a" is an integer from 100 to 100,000, the subscript "b" is an integer from 1 to 10, and the sum a+b is from 101 to 100,000) (A-2) from 0 to 90 parts by weight of an organopolysiloxane gum of average compositional formula below which is capped at both ends of the molecular chain with monoalkenyldialkylsiloxy groups and has an alkenyl group content of from 0.001 to 10 mol% (wherein R 1, R 2 and R 3 are the same as above, the subscript "a" is an integer from 100 to 100,000, the integer "b" is an integer from 0 to 1,000, and the sum a+b is from 100 to 100,000); an organohydrogenpolysiloxane of average compositional formula below which has at least two silicon-bonded hydrogen atoms per molecule R 4 p H q SiO (4-p-q)/2 (wherein each R 4 is a like or unlike monovalent hydrocarbon group of 1 to 12 carbon atoms, and p and q are positive numbers which satisfy the conditions 0 < p < 3, 0 < q ≤ 3 and 0 < p+q ≤ 3), in an amount corresponding to from 0.5 to 10 moles of hydrosilyl groups in component per mole of the total amount of alkenyl groups in component; from 50 to 100 parts by weight of carbon black having an average primary particle size of from 100 to 350 nm; from 5 to 100 parts by weight of a reinforcing fumed silica having a specific surface area as measured by the BET adsorption method of at least 50 m 2 g; and a platinum family metal catalyst in an amount, based on the weight of the platinum family metal, of from 1 ppm by weight to 1 wt% relative to the organopolysiloxane of component. an alkenyl group-containing organopolysiloxane gum consisting of components (A-1) and (A-2) below in a total amount of 100 parts by weight (A-1) 10 to 100 parts by weight of an organopolysiloxane gum of average compositional formula below which is capped at both ends of the molecular chain with trialkenylsiloxy groups and has an alkenyl group content of 0.25 mol% or less (wherein each R 1 is a like or unlike alkenyl group of 2 to 8 carbon atoms, each R 2 is a like or unlike group selected from the group consisting of alkyl groups of 1 to 20 carbon atoms and aromatic hydrocarbon groups of 6 to 20 carbon atoms, each R 3 is a like or unlike group selected from R 1 and R 2, the subscript "a" is an integer from 100 to 100,000, the subscript "b" is an integer from 1 to 10, and the sum a+b is from 101 to 100,000) (A-2) from 0 to 90 parts by weight of an organopolysiloxane gum of average compositional formula below which is capped at both ends of the molecular chain with monoalkenyldialkylsiloxy groups and has an alkenyl group content of from 0.001 to 10 mol% (wherein R 1, R 2 and R 3 are the same as above, the subscript "a" is an integer from 100 to 100,000, the integer "b" is an integer from 0 to 1,000, and the sum a+b is from 100 to 100,000); (A-1) 10 to 100 parts by weight of an organopolysiloxane gum of average compositional formula below which is capped at both ends of the molecular chain with trialkenylsiloxy groups and has an alkenyl group content of 0.25 mol% or less (wherein each R 1 is a like or unlike alkenyl group of 2 to 8 carbon atoms, each R 2 is a like or unlike group selected from the group consisting of alkyl groups of 1 to 20 carbon atoms and aromatic hydrocarbon groups of 6 to 20 carbon atoms, each R 3 is a like or unlike group selected from R 1 and R 2, the subscript "a" is an integer from 100 to 100,000, the subscript "b" is an integer from 1 to 10, and the sum a+b is from 101 to 100,000) (A-2) from 0 to 90 parts by weight of an organopolysiloxane gum of average compositional formula below which is capped at both ends of the molecular chain with monoalkenyldialkylsiloxy groups and has an alkenyl group content of from 0.001 to 10 mol% (wherein R 1, R 2 and R 3 are the same as above, the subscript "a" is an integer from 100 to 100,000, the integer "b" is an integer from 0 to 1,000, and the sum a+b is from 100 to 100,000); an organohydrogenpolysiloxane of average compositional formula below which has at least two silicon-bonded hydrogen atoms per molecule R 4 p H q SiO (4-p-q)/2 (wherein each R 4 is a like or unlike monovalent hydrocarbon group of 1 to 12 carbon atoms, and p and q are positive numbers which satisfy the conditions 0 < p < 3, 0 < q ≤ 3 and 0 < p+q ≤ 3), in an amount corresponding to from 0.5 to 10 moles of hydrosilyl groups in component per mole of the total amount of alkenyl groups in component; from 50 to 100 parts by weight of carbon black having an average primary particle size of from 100 to 350 nm; from 5 to 100 parts by weight of a reinforcing fumed silica having a specific surface area as measured by the BET adsorption method of at least 50 m 2 g; and a platinum family metal catalyst in an amount, based on the weight of the platinum family metal, of from 1 ppm by weight to 1 wt% relative to the organopolysiloxane of component.