A silicone composition comprising (i) alkenyl group-containing organopolysiloxanes consisting of components and; and (ii) components to: 100 parts by mass of a linear, branched, or network organopolysiloxane having a vinyl value of 0.01 mol/100 g or more and 0.04 mol/100 g or less, and a viscosity of 100 mm 2 /sec or more and 500 mm 2 /sec or less as determined with an Ostwald viscometer at 25°C, which organopolysiloxane is represented by formula wherein each of the terminals thereof has one or more alkenyl groups: (R 1 R 2 2 SiO 1/2) a (R 2 2 SiO) 3 (R 2 SiO 3/2) c (SiO 4/2) d wherein R 2 is, independently of each other, a substituted or unsubstituted, monovalent hydrocarbon group having no aliphatic unsaturated bond and having 1 to 16 carbon atoms; R 1 is an alkenyl group having 2 to 10 carbon atoms; and a to d are integers satisfying the equations: 2 ≤ a ≤ 18, 10 ≤ b ≤ 400, 0 ≤ c ≤ 8, 0 ≤ d ≤ 8, and 0 ≤ c + d ≤ 8; 0.01 to 3 parts by mass of a linear, branched, or network organopolysiloxane having a vinyl value of 0.2 mol/100 g or more and 1.2 mol/100 g or less, and a viscosity of 2 mm 2 /sec or more and 60 mm 2 /sec or less as determined with an Ostwald viscometer at 25°C, which organopolysiloxane is represented by formula wherein each of the terminals thereof has one or more alkenyl groups: (R 1 R 2 2 SiO 1/2) e (R 2 2 SiO) f (R 2 SiO 3/2) g (SiO 4/2) h wherein R 2 is, independently of each other, a substituted or unsubstituted, monovalent hydrocarbon group having no aliphatic unsaturated bond and having 1 to 16 carbon atoms; R 1 is an alkenyl group having 2 to 10 carbon atoms; and e to h are integers satisfying the equations: 3 ≤ e ≤ 24, 0 ≤ f ≤ 60, 1 ≤ g ≤ 22, 0 ≤ h ≤ 11, and 1 ≤ g + h ≤ 22; an organohydrogenpolysiloxane having an amount of 1 mol/100 g or more and 2 mol/100 g or less of an SiH group, wherein the ratio of the number of the SiH groups in component to the total number of the alkenyl groups in components and is 1 to 5; 0.01 to 10 parts by mass of an addition-reaction control agent, relative to total 100 parts by mass of components,, and; and a catalytic amount of a platinum group metal catalyst. 100 parts by mass of a linear, branched, or network organopolysiloxane having a vinyl value of 0.01 mol/100 g or more and 0.04 mol/100 g or less, and a viscosity of 100 mm 2 /sec or more and 500 mm 2 /sec or less as determined with an Ostwald viscometer at 25°C, which organopolysiloxane is represented by formula wherein each of the terminals thereof has one or more alkenyl groups: (R 1 R 2 2 SiO 1/2) a (R 2 2 SiO) 3 (R 2 SiO 3/2) c (SiO 4/2) d wherein R 2 is, independently of each other, a substituted or unsubstituted, monovalent hydrocarbon group having no aliphatic unsaturated bond and having 1 to 16 carbon atoms; R 1 is an alkenyl group having 2 to 10 carbon atoms; and a to d are integers satisfying the equations: 2 ≤ a ≤ 18, 10 ≤ b ≤ 400, 0 ≤ c ≤ 8, 0 ≤ d ≤ 8, and 0 ≤ c + d ≤ 8; 0.01 to 3 parts by mass of a linear, branched, or network organopolysiloxane having a vinyl value of 0.2 mol/100 g or more and 1.2 mol/100 g or less, and a viscosity of 2 mm 2 /sec or more and 60 mm 2 /sec or less as determined with an Ostwald viscometer at 25°C, which organopolysiloxane is represented by formula wherein each of the terminals thereof has one or more alkenyl groups: (R 1 R 2 2 SiO 1/2) e (R 2 2 SiO) f (R 2 SiO 3/2) g (SiO 4/2) h wherein R 2 is, independently of each other, a substituted or unsubstituted, monovalent hydrocarbon group having no aliphatic unsaturated bond and having 1 to 16 carbon atoms; R 1 is an alkenyl group having 2 to 10 carbon atoms; and e to h are integers satisfying the equations: 3 ≤ e ≤ 24, 0 ≤ f ≤ 60, 1 ≤ g ≤ 22, 0 ≤ h ≤ 11, and 1 ≤ g + h ≤ 22; an organohydrogenpolysiloxane having an amount of 1 mol/100 g or more and 2 mol/100 g or less of an SiH group, wherein the ratio of the number of the SiH groups in component to the total number of the alkenyl groups in components and is 1 to 5; 0.01 to 10 parts by mass of an addition-reaction control agent, relative to total 100 parts by mass of components,, and; and a catalytic amount of a platinum group metal catalyst.