Abstract: Two-piece solid golf balls having an improved initial velocity are disclosed. The core is obtained by curing a composition comprising (a) 100 parts by weight of polybutadiene, (b) 9-20 parts by weight of a polyfunctional unsaturated ester, (c) 5-10 parts by weight of methacrylic acid and/or acrylic acid, the total amount of the ingredients (b) and (c) being 15-30 parts by weight and the weight ratio of the ingredient (b)/the ingredient (c) being 55/45-80/20, (d) 20-80 parts by weight of a zinc compound and (e) 0.5-5 parts by weight of an alkyl peroxide. The cover comprises (f) 100 parts by weight of a metal salt of a copolymer of ethylene and unsaturated carboxylic acid, said metal salt having a loss tangent of lower than 0.08, and (g) 1-5 parts by weight of an inorganic filler.

Abstract: An ethylene-propylene copolymer rubber composition having a high Young's modulus, which comprises 100 parts by weight of a mixture of the following ingredients (a) and (b) in a weight ratio of ingredient (a)/ingredient (b) of 67/33-50/50, said ingredient (a) being an ethylene-propylene copolymer having a Mooney viscosity of at least 75, said ingredient (b) being divinylbenzene, (c) 0.3-2.5 parts by weight of an organic peroxide, and (d) 0.01-0.25 part by weight of sulfur, and the homogeneous rubber composition cured at 120.degree.-180.degree.C having a Young's modulus of 200-500 Kg/cm.sup.2, a tensile strength of at least 200 Kg/cm.sup.2, an elongation of at least 300%, a tear energy of at least 10 Kg/cm and retentions of Young's modulus and tensile strength at 70.degree.C of at least 50%.