A multiarm star-shaped polystyrene (PS) was prepared from polystyrene-block-poly(glycidyl methacrylate) (PS-b-PGMA) by combination of atom transfer radical polymerization (ATRP) and cationic-ring opening polymerization (CROP). First, ATRP of styrene was carried out using ethyl 2-bromoisobutyrate (EIBr) as the initiator and copper halide (CuBr) with N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA) as the catalyst system in bulk at 110 degrees C. Then, previously obtained PS was used as a macroinitiator for ATRP of glycidyl methcrylate (GMA) using CuCl/PMDETA as the catalyst system in anisole at 60 degrees C. This produced an AB-type di-block co-polymer (PS-b-PGMA) with a controlled molecular weight and low polydispersity (M-w/M-n = 1. 15). As a third step, CROP of pendant oxirane rings of PS-b-PGMA di-block co-polymer led to a multiarm star-shaped PS in a novel approach. The obtained polymers were characterized by gel-permeation chromatography and H-1-NMR.