Abstract: Well-defined cyclic diblock copolymer of c(PI-b-PS) (PI: polyisoprene, PS: polystyrene) with controlled molecular weight(Mn) and polydispersity index (PDI) was synthesized by combination of anionic polymerization high vacuum techniques(HVTs) and Glaser coupling (cyclization) reaction. Initially, well-defined dihydroxyl linear diblock copolymer of HO-PI-b-PS-OH type was synthesized via anionic polymerization using t-butyl-dimethylsilyloxypropyllithium as initiator. Furthermore, acyclic diblock copolymer of c(PS-b-PI) was successfully obtained in high yield. The synthetic procedure involves: a) deprotection of t-butyl-dimethylsilyloxypropyl functional end group, b) esterification of -OH groups to introduce two alkynyl groups and c) Glaser coupling reaction, under high dilution. All intermediates and final products were characterized by gel permeation chromatography (GPC) and proton nuclear magnetic resonance spectroscopy (1H NMR).