A multi-piece solid golf ball composed of a solid core having an inner core layer and an outer core layer encased by a cover including at least an inner cover layer and an outer cover layer. The inner core layer has a JIS-C cross-sectional hardness of from 60 to 83 at any single point on a cross-section, and has a cross-sectional hardness difference between any two points on the cross-section of within ±5. 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. And, the outer cover layer has the specific Shore D hardness, which is lower than that of the inner cover layer.