Polytetrahydrofuran (PTHF)/poly(1,3-dioxepane) (PDOP)/polystyrene (PSt) ABC miktoarm star copolymers were synthesized by combination of cationic ring-opening polymerization (CROP) and atom transfer radical polymerization. Two different functional groups, carboxylic acid and CHBr, were capped at one end of PTHF through the reaction of PTHF-OH with 2-bromosuccinic anhydride (BSA). After PTHF-OOCCHBrCH2COOH reacted with thionyl chloride, block copolymer PTHF-b-PDOP was synthesized by CROP of DOP at -30 to -35degreesC with PTHF-OOCCHBrCH2COCl and AgClO4 as catalyst. Finally, (PTHF) (PDOP)-Br was used to initiate the polymerization of St in the presence of CuBr and bipyridine at 110 degreesC, and ABC miktoarm star polymer, s-[(PTHF) (PDOP) (PSt)] was successfully prepared. The copolymers obtained were characterized by H-1 NMR and gel permeation chromatography measurements.