Star shaped polystyrenes of mono-, tri-, and tetraarms were synthesized by atomtransfer radical polymerization (ATRP) using initiators, which were obtained by the reaction of trichloroactyl chloride with phenol, 1,3,5-tris (2-hydroxyethyl)cyanuric acid, and pentaerythritol, respectively. The structures of initiators were identified by means of ^{1}H$ NMR and $^{13}C$ NMR. Living nature of the polymerization was confirmed by kinetic and structural analyses. It has been found that the polymerization behavior in tri-armed polymer synthesis was nearer to ideal living polymerization than that in the synthesis of tetra-armed polymer.