The cationic propagation ends of telechelic living poly(tetrahydrofuran) (polyTHF) were reduced into anionic ones by 4 equiv of samarium(II) iodide in the presence of hexamethylphosphoramide (HMPA). NMR analyses indicated the quantitative reduction of poly(THF) into the telechelic poly(THF) macroanion without any serious side reaction. The transformed telechelic poly(THF) macroanion initiated the polymerization of tert-butyl methacrylate (TBMA) with quantitative initiator efficiency resulting in the production of ABA-type triblock copolymer of TBMA and THF with a narrow molecular weight distributions (<1.19). Any homopolymer of THF or TBMA was not detected. The unit ratio of THF and TBMA could be facilely controlled by both the poly(THF) macroanion and the amount of TBMA.