Monocyclopendienyltitanium trichloride (CpTiCl3) was supported on polymer carriers with different hydroxyl contents, and the supported catalysts were used for styrene polymerization. The supported catalysts exhibited high activity even at low Al/Ti ratios and increased the molecular weight of the products, indicating that polymer carriers could stabilize the active sites. The polymers prepared with unsupported and supported catalysts were extracted with boiling n-butanone and characterized by carbon nuclear magnetic resonance (C-13 NMR) and differential scanning calorimetry. The polymers obtained by supported catalysts had a high fraction of boiling n-butanone-insoluble part and high melting temperatures, but C-13 NMR results showed that syndiotacticity decreased compared with that of polymers prepared with an unsupported catalyst. ESR study on the supported catalysts confirmed that the active sites supported on the carrier dropped into the solution and formed active sites the same as those in the unsupported system when they reacted with methylaluminoxane. C-13 NMR analysis showed that the polymerization mechanism of the supported active sites was an active-site controlled mechanism instead of a chain-end controlled mechanism of the unsupported active sites.