The invention provides a multi-piece solid golf ball composed of a solid core encased by a cover of one or more layer, which solid core has an inner core layer and an outer core layer. The inner core layer is formed primarily of a specific, highly neutralized, ionomeric resin composition, has a diameter of from 10 to 38 mm, and has a cross-sectional hardness difference of within ±5 between any two points on a cross-section formed by cutting the inner core layer in half. The outer core layer is formed of a rubber composition made primarily of polybutadiene rubber. The solid core has a diameter of from 30 to 42 mm. The sum of the respective hardnesses at the center of the inner core layer, at the outer core layer 1 mm outside a boundary between the inner core layer and the outer core layer, at the inner core layer 1 mm inside the boundary, and at the surface of the outer core layer is set to a value in a range of from 260 to 360. Such a golf ball is able to achieve an increased distance.