Monodisperse silica particles (SiPs) were surface‐modified with a newly designed silane coupling agent comprising a triethoxysilane and an alkyl halide, namely, 6‐(triethoxysilyl)hexyl 2‐bromopropionate, which was further treated with potassium O‐ethyl dithiocarbonate (PEX) to immobilize xanthate molecules on the particle surfaces. Surface‐initiated macromolecular design via interchange of xanthates (MADIX) polymerization of vinyl acetate (VAc) was conducted with the xanthate‐functionalized SiPs. The polymerization was well controlled and produced SiPs coated with poly(vinyl acetate) (PVAc) with a well‐defined target molar mass and a graft density of about 0.2 chains nm−2. Dynamic light scattering and TEM measurements revealed that the hybrid particles were highly dispersible in good solvents without any aggregation. The PVAc brushes were hydrolyzed with hydrochloric acid to produce poly(vinyl alcohol) brushes on the SiP surfaces. In addition, the number of xanthate molecules introduced on the SiP surfaces could be successfully controlled by adjusting the concentration of PEX. Thus, the SiPs have two functionalities: xanthates able to act as a MADIX chain‐transfer agent and alkyl bromide initiation sites for atom transfer radical polymerization (ATRP). By using these unique bifunctional particles, mixed polymer brushes were constructed on the SiPs by MADIX of VAc followed by ATRP of styrene or methyl methacrylate.