Multi-piece solid golf ball

A multi-piece solid golf ball comprising a solid core consisting of a center core and an outer core, an inner cover layer and an outer cover layer, wherein the solid core is molded from a rubber composition comprising

• 100 parts by weight of a base rubber composed of (a) 35 to 70 wt % of a polybutadiene having a cis-1,4 content of at least 95% and a 1,2 vinyl content of at most 1.3%, having a viscosity η at 25° C. as a 5 wt % solution in toluene of up to 400 mPa·s, being synthesized using a rare-earth catalyst, in combination with (b) 30 to 65 wt % of a diene rubber other than Component (a),
• (c) 10 to 60 parts by weight of an unsaturated carboxylic acid or a metal salt thereof or both,
• (d) 0.1 to 5 parts by weight of an organosulfur compound,
• (e) 5 to 80 parts by weight of an inorganic filler, and
• (f) 0.1 to 5 parts by weight of an organic peroxide;
• the center core has a JIS-C hardness of 40 to 60 on its center and a JIS-C hardness of 55 to 75 on its surface and the difference therebetween is in the range of 10 to 20, the outer core is harder than the surface hardness of the center core, the cross-sectional hardness of 1 mm outside from the border between the center core and the outer core is from 65 to 85 on a JIS-C hardness, a surface of the outer core has a JIS-C of 75 to 95,
• the inner cover layer has a Shore D hardness of 50 to 80, the outer cover layer has a Shore D hardness of 35 to 60, and
• the outer cover layer has a lower Shore D hardness than the inner cover layer,
• wherein the polybutadiene (a) satisfies relationship:
• 10B+5≦A≦10B+60, wherein A is the Mooney viscosity (ML1+4 (100° C.)) of the polybutadiene and B is the ratio Mw/Mn between the weight-average molecular weight Mw and the number-average molecular weight Mn of the polybutadiene, and
• wherein the diene rubber (b) includes 30 to 100 wt % of a second polybutadiene which has a cis-1,4 content of at least 60% and a 1,2 vinyl content of at most 5%, has a Mooney viscosity (ML1+4 (100° C.)) of not more than 55, and satisfies the relationship:
• η≦20A−550,
• wherein A is the Mooney viscosity (ML1+4 (100° C.)) of the second polybutadiene and η is the viscosity of the second polybutadiene, in mPa·s, at 25° C. as a 5 wt % solution in toluene.