Propene polymerization was conducted with the [t-BuNSiMe(2)Flu]TiMe2/B(C6F5)(3) catalyst at -50 degrees C at various concentrations of propene. The polymerization proceeds in a living manner regardless of the propene concentration employed. Molecular weight of polymer obtained in a certain polymerization time with low monomer conversion increases with increasing concentration of propene. The logarithmic plot of molecular weight against propene concentration gives a straight line with a slope of 1.8, which indicates that the propagation rate is almost of second order with respect to propene concentration.