The polymerization of vinyl chloride (VC) with half-titanocene/methylaluminoxane (MAO) catalysts is investigated. The polymerization of VC with the Cp*Ti(OCH3)(3)/MAO catalyst (Cp* = eta(5)-pentamethylcyclopentadienyl) afforded high-molecular-weight poly(vinyl chloride) (PVC) in good yields, although the polymerization proceeded at a slow rate. With the Cp*TiCl3/MAO catalyst, the polymer was also obtained, but the polymer yield was lower than that with the Cp*Ti(OCH3)(3)/MAO catalyst. The polymerization of VC with the Cp*Ti(OCH3)(3)/MAO catalyst was influenced by the MAO/Ti mole ratio and reaction temperature, and the optimum was observed at the MAO/Ti mole ratio of about 10. The optimum reaction temperature of VC with the CP*Ti(OCH3)(3/)MAO catalyst was around 20 degreesC. The stereoregularity of PVC obtained with the Cp*Ti(OCH3)(3)/MAO catalyst was different from that obtained with azobisisobutyronitrile, but highly stereoregular PVC could not be synthesized. From the elemental analyses, the H-1 and C-13 NMR spectra of the polymers, and the analysis of the reduction product from PVC to polyethylene, the polymer obtained with Cp*Ti(OCH3)(3)/MAO catalyst consisted of only regular head-to-tail units without any anomalous structure, whereas the Cp*TiCl3/MAO catalyst gave the PVC-bearing anomalous units. The polymerization of VC with the Cp*Ti(OCH3)(3)/MAO catalyst did not inhibit even in the presence of radical inhibitors such as 2,2,6,6,-tetrametylpiperidine-1-oxyl, indicating that the polymerization of VC did not proceed via a radical mechanism.