The present invention provides a multi-piece solid golf ball having a core, an envelope encasing the core, an intermediate layer encasing the envelope, and a cover which encases the intermediate layer and has formed on a surface thereof a plurality of dimples. The surface hardness of the core has a JIS-C hardness value of 40 to 95, the center hardness of the core has a JIS-C hardness value of 30 to 72, and the hardness difference therebetween is from 4 to 14. The envelope is composed of at least two layers. The core is formed primarily of a rubber material. The envelope, intermediate layer and cover are each formed primarily of the same or different resin materials. An optimized surface hardness relationship exists between the core, a Sphere I composed of the core encased by the envelope layers, a Sphere II composed of the core encased by the envelope layers and the intermediate layer, and a Sphere III composed of the core encased by the envelope layers, the intermediate layer and the cover. The golf ball has an outstanding flight performance and controllability which are acceptable to professionals and other skilled players, in addition to which it has an excellent durability to cracking under repeated impact and an excellent scuff resistance.