A photocurable composition comprising (a) a silsesquioxane having a cyano group, (b) an ethylenically unsaturated monofunctional monomer having a cyano group, (c) an ethylenically unsaturated polyfunctional monomer, and (d) a photo-polymerization initiator, component (a) being a silsesquioxane having the general formula: (NC-A-SiO 3/2) m (NC-A-SiRO 2/2) n (NC-A-SiR 2 O 1/2) p (G-B-SiO 3/2) q (G-B-SiR 1 O 2/2) r (G-B-SiR 1 2 O 1/2) s wherein A and B are each independently a C 1 -C 10 divalent hydrocarbon group, R and R 1 are each independently a C 1 -C 6 monovalent hydrocarbon group, C 1 -C 3 alkoxy group, hydroxyl group or C 3 -C 20 triorganosiloxy group, G is a C 1 -C 8 alkyl group or C 1 -C 3 alkoxy group, in which one or two hydrogen atoms are substituted by a monovalent substituent selected from the group consisting of a carboxyl group, C 2 -C 4 ester group, hydroxyl group, C 2 -C 6 epoxide-containing group, C 3 -C 6 α,β-unsaturated acyloxy group, C 2 -C 3 alkenyl group, and C 4 -C 8 acid anhydride-containing group, m, n, p, q, r and s are each independently an integer of 0 to 200, the sum m+q is at least 4, the sum m+n+p is 4 to 200, and the sum m+n+p+q+r+s is 4 to 200, and wherein component (b) is 2-cyanoethyl (meth)acrylate, 3-cyanopropyl (meth)acrylate, 4-cyanophenyl (meth)acrylate, or (meth) acrylonitrile. (a) a silsesquioxane having a cyano group, (b) an ethylenically unsaturated monofunctional monomer having a cyano group, (c) an ethylenically unsaturated polyfunctional monomer, and (d) a photo-polymerization initiator, component (a) being a silsesquioxane having the general formula: (NC-A-SiO 3/2) m (NC-A-SiRO 2/2) n (NC-A-SiR 2 O 1/2) p (G-B-SiO 3/2) q (G-B-SiR 1 O 2/2) r (G-B-SiR 1 2 O 1/2) s wherein A and B are each independently a C 1 -C 10 divalent hydrocarbon group, R and R 1 are each independently a C 1 -C 6 monovalent hydrocarbon group, C 1 -C 3 alkoxy group, hydroxyl group or C 3 -C 20 triorganosiloxy group, G is a C 1 -C 8 alkyl group or C 1 -C 3 alkoxy group, in which one or two hydrogen atoms are substituted by a monovalent substituent selected from the group consisting of a carboxyl group, C 2 -C 4 ester group, hydroxyl group, C 2 -C 6 epoxide-containing group, C 3 -C 6 α,β-unsaturated acyloxy group, C 2 -C 3 alkenyl group, and C 4 -C 8 acid anhydride-containing group, m, n, p, q, r and s are each independently an integer of 0 to 200, the sum m+q is at least 4, the sum m+n+p is 4 to 200, and the sum m+n+p+q+r+s is 4 to 200, and wherein component (b) is 2-cyanoethyl (meth)acrylate, 3-cyanopropyl (meth)acrylate, 4-cyanophenyl (meth)acrylate, or (meth) acrylonitrile. wherein A and B are each independently a C 1 -C 10 divalent hydrocarbon group, R and R 1 are each independently a C 1 -C 6 monovalent hydrocarbon group, C 1 -C 3 alkoxy group, hydroxyl group or C 3 -C 20 triorganosiloxy group, G is a C 1 -C 8 alkyl group or C 1 -C 3 alkoxy group, in which one or two hydrogen atoms are substituted by a monovalent substituent selected from the group consisting of a carboxyl group, C 2 -C 4 ester group, hydroxyl group, C 2 -C 6 epoxide-containing group, C 3 -C 6 α,β-unsaturated acyloxy group, C 2 -C 3 alkenyl group, and C 4 -C 8 acid anhydride-containing group, m, n, p, q, r and s are each independently an integer of 0 to 200, the sum m+q is at least 4, the sum m+n+p is 4 to 200, and the sum m+n+p+q+r+s is 4 to 200, and wherein component (b) is 2-cyanoethyl (meth)acrylate, 3-cyanopropyl (meth)acrylate, 4-cyanophenyl (meth)acrylate, or (meth) acrylonitrile.