The living cationic polymerization of a novel bicyclic conjugated diene monomer, tetrahydroindene (THI) (bicyclo[4.3.0]-2,9-nonadiene), was achieved using the SnCl4-based initiating system, in which the Lewis acid works as an activator for the dormant C-Cl terminal originating from the hydrogen chloride adduct of the 2-chloroethyl vinyl ether as an initiator ( 1) in the presence of a nucleophilic additive such as ethyl acetate. The number-average molecular weights of the obtained polymers increased in direct proportion to the monomer conversion, and the MWDs were narrow throughout the reactions (M-w/M-n similar to 1.2). The well-defined terminal structure of the obtained poly(THI) was confirmed by the H-1 NMR and MALDI-TOF MS analysis, which shows the presence of the initiator moiety at the R end and the chlorine at the omega end. The living cationic block copolymerization of isobutyl vinyl ether (IBVE) followed by THI led to the di- and triblock copolymers consisting of the hard nonpolar THI and soft polar IBVE segments for possible application of the triblock copolymer as a thermoplastic elastomer.