Polymerization of propene was conducted by [t-BuNSiMe(2)Flu]TiMe2-based catalysts at -50 degrees C in the presence of trioctylaluminum. When B(C6F5)(3) was used as a cocatalyst, polymer yield monotonically increased with increasing polymerization time. The polypropene obtained showed narrow molecular weight distribution, and the number average molecular weight of the polymer linearly increased against the polymer yield. In addition, the number of polymer chains, which was approximately a half the number of Ti used, was almost constant during the polymerization. The living nature of the [t-BuNSiMe(2)Flu]TiMe2 catalyst depended on polymerization temperature and cocatalyst. Deactivation occurred at 0 degrees G or even at -50 degrees C when Ph3CB(C6F5)(4) was used in place of B(C6F5)(3). C-13 NMR analysis of the polymer indicated that the living polymerization proceeded highly regiospecifically via I,a-insertion to give syndiotactic-rich polymer. Polymerization of I-hexene with [t-BuNSiMe(2)Flu]TiMe2/B(C6F5)(3) also proceeded in a living manner at -50 degrees C, and highly regioregular and syndiotactic-rich polymer was obtained.