Well-defined homopolymer and diblock copolymer were prepared by RAFT polymerization mediated by Z-supported chain transfer agent (CTA) onto silica particles. Silica-supported 3-(methoxycarbonylphenylmethylsulfanylthiocarbonylsulfanyl) propionic acid (Si-MPPA) was used to mediate RAFT polymerization of methyl acrylate, methyl methacrylate, butyl acrylate, and styrene to produce homopolymer grafted silica. The introduction of a free CTA such as MPPA and 2-(2-cyanopropyl) dithiobenzoate (CPDB) in solution during polymerization could significantly improve the control on molecular weight and polydispersity of grafted polymers, and the polymerization in the presence of CPDB was more controlled than that using MPPA. The resultant homopolymer grafted silica was utilized as a macro-CTA to mediate chain extension polymerization, and a series of diblock copolymer grafted silica hybrids were prepared. Aminolysis of the polymers allowed the recovery of the polymeric chains showing 100% chain extension, as illustrated by the complete shift of GPC traces and low polydispersity (M-w/M-n < 1.2). This efficient chain extension polymerization confirmed the original macro-CTAs had living homopolymer chains covalently attached to the surface.