Cia-specific living polymerizations of 1,3-butadiene (BD) catalyzed by the catalyst system composed of C5H4RTiCl3 (4a, R = H; 4b, R = n-butyl; 4c, R = isopropyl; 4d, R = tert-butyl; 4e, R = trimethylsilyl) with methylaluminoxane (MAO) to give polyBDs with narrow molar mass distribution and high cis content are described. Polybutadienes (polyBDs) prepared by the catalyst at -25 degrees C are monodispersed (M-w/M-n = 1.04-1.05) in all cases. From the comparison with propagation rate constants (k(p)), the order of polymerization activity was as follows: 4d > 4e > 4e > 4b = 4a. The microstructures of polyBDs were all dominated by the cis configuration. The complex 4d having bulky tert-butyl group showed higher cis specicficity. Both k(p)s and cis specificity in the polymerization of ED were strongly affected by the substituents introduced on the cyclopentadienyl ring.