A curable composition, comprising: a first organopolysiloxane (A) having an average composition according to Formula 1; and a second organopolysiloxane (B) comprising an alkenyl group, an epoxy group and an aryl group: [Formula 1] (R 1 R 2 2 SiO 1/2 ) a (R 3 R 4 SiO 2/2 ) b (R 5 SiO 3/2 ) c (SiO 2 ) d where R 1 is a monovalent hydrocarbon group having at least two carbon atoms, R 2 is an alkyl group having 1 to 4 carbon atoms, R 3 and R 4 are each independently an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms or an aryl group having 6 to 25 carbon atoms, R 5 is an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 25 carbon atoms, with the proviso that at least one of R 1 , R 3 and R 4 is an alkenyl group; a is a positive number, b is a positive number, c is a positive number, d is 0 or a positive number, b/a is 5 or more, and b/c is 5 or more, wherein b/(a+b+c+d) of the Formula 1 is 0.5 or more, wherein the first organopolysiloxane (A) having the average composition formula of Formula 1 includes aryl groups binding to a silicon atom and all of the aryl groups that bind to silicon atoms of the first organopolysiloxane (A) having the average composition formula of Formula 1 bind to silicon atoms of D and T unit, wherein a molar ratio (Ar/Si) of the aryl group (Ar) binding to the silicon atom with respect to a total of silicon atoms (Si) in the first organopolysiloxane (A) is 0.3 or more, and wherein a molar ratio (Ar-D/Si) of the aryl group (Ar-D) binding to a silicon atom of a D unit with respect to a total of silicon atoms (Si) of the first organopolysiloxane (A) is 0.2 or more, wherein the D unit is represented by R 3 R 4 SiO 2/2 and the T unit is represented by R 5 SiO 3/2 . a first organopolysiloxane (A) having an average composition according to Formula 1; and a second organopolysiloxane (B) comprising an alkenyl group, an epoxy group and an aryl group: [Formula 1] (R 1 R 2 2 SiO 1/2 ) a (R 3 R 4 SiO 2/2 ) b (R 5 SiO 3/2 ) c (SiO 2 ) d where R 1 is a monovalent hydrocarbon group having at least two carbon atoms, R 2 is an alkyl group having 1 to 4 carbon atoms, R 3 and R 4 are each independently an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms or an aryl group having 6 to 25 carbon atoms, R 5 is an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 25 carbon atoms, with the proviso that at least one of R 1 , R 3 and R 4 is an alkenyl group; a is a positive number, b is a positive number, c is a positive number, d is 0 or a positive number, b/a is 5 or more, and b/c is 5 or more, wherein b/(a+b+c+d) of the Formula 1 is 0.5 or more, wherein the first organopolysiloxane (A) having the average composition formula of Formula 1 includes aryl groups binding to a silicon atom and all of the aryl groups that bind to silicon atoms of the first organopolysiloxane (A) having the average composition formula of Formula 1 bind to silicon atoms of D and T unit, wherein a molar ratio (Ar/Si) of the aryl group (Ar) binding to the silicon atom with respect to a total of silicon atoms (Si) in the first organopolysiloxane (A) is 0.3 or more, and wherein a molar ratio (Ar-D/Si) of the aryl group (Ar-D) binding to a silicon atom of a D unit with respect to a total of silicon atoms (Si) of the first organopolysiloxane (A) is 0.2 or more, wherein the D unit is represented by R 3 R 4 SiO 2/2 and the T unit is represented by R 5 SiO 3/2 . <EOS>