To obtain well-defined dendritic-graft copolymer grafted silica nanoparticles (SN-HBP-PMMA), the surface halogen atom of the hyperbranched polymer grafted silica nanoparticles (SN-HBP), by surface-initiated self-condensing vinyl polymerization (SI-SCVP) of p-chloromethyl styrene (CMS) from functionalized silica nanoparticles, was used as initiator for the surface-initiated atom transfer radical polymerization (SI-ATRP) of methyl methacrylate (MMA) for the first time. The well-defined hyperbranched polymer and the dendritic-graft copolymer grafted were validated by H-1 NMR analysis. And, the dispersibility of the well-defined polymer grafted silica nanoparticles was investigated with a transmission electron microscope (TEM).