A variety of polymer microspheres were successfully synthesized by the surface-initiated atom transfer radical polymerization (SI-ATRP) of monomers by using monodisperse polymer microsphere having benzyl halide moiety as a multifunctional polymeric initiator. First, a series of monodisperse polymer microsphere having benzyl chloride with variable monomer ratio (P(St-DVB-VBC)) were synthesized by the precipitation polymerization of styrene (St), divinylbenzene (DVB), and 4-vinylbenzyl chloride (VBC). Next, hairy polymer microspheres were synthesized by the surface-initiated ATRP of various monomers with P(St-DVB-VBC) microsphere as a multifunctional polymeric initiator. The hair length determined by the SEC analysis of free polymer was increased with the increase of M/I. These hairy polymer microspheres were characterized by SEM, FT-IR, and Cl content measurements.Among many controlled "grafting from" polymerizations, controlled/"living" radical polymerization techniques (CRPs) (e.g., nitroxide-mediated radical polymerization, 34 atom transfer radical polymerization (ATRP), [35][36][37] and RAFT polymerization [38][39][40] are widely used because of their good control over the polymer chain length, grafting densities, broad applicability to a wide range of monomers, and mild reaction conditions. These living techniques are able to generate grafted homopolymers, copolymers and block copolymers.Additional supporting information may be found in the online version of this article.