Abstract: The invention provides a golf ball having a core and a cover of one layer or a plurality of layers, wherein the core is formed of a material molded under heat from a rubber composition containing (A) a base rubber, (B) an organic peroxide, and (C) water and/or a metal monocarboxylate, and has a hysteresis loss of 50% or less when compressed at a load cell speed of 500 mm/min and under a constant load of 5,000 N.

Abstract: The invention provides a multi-piece solid golf ball composed of a solid core encased by a cover of two or more layers, which solid core has an inner core layer and an outer core layer, and cover has an inner cover layer and an outer cover layer. The inner core layer is formed primarily of a thermoplastic resin, has a diameter of from 21 to 38 mm, has a JIS-C cross-sectional hardness of from 60 to 83 at any single point on a cross-section obtained by cutting the inner core layer in half, and has a cross-sectional hardness difference between any two points on the cross-section of within ±5. The outer core layer is formed of a rubber composition made primarily of polybutadiene rubber. The solid core has a diameter of from 35 to 42 mm. The ball has specific relationships between the hardness of the inner core layer 1 mm inside a boundary between the inner core layer and the outer core layer, the hardness of the outer core layer 1 mm outside the boundary, and the surface hardness of the outer core layer.