In the case of the oxidative polymerization of 3-hexylthiophene (3HT) with FeCl3, FeCl3 is always required at a concentration four times higher than that of 3HT to produce high-molecular-weight P3HT. In order to avoid the use of excess FeCl3, it was considered that an oxidizer could assist the catalytic oxidative polymerization by oxidizing Fe2+ to Fe3+. To determine an effective oxidation agent (Fe2+ to Fe3+), various oxidizers (Cl-2, BPO, H2O2, ZrCl4, and (NH4)(2)Ce(NO3)(6)) were examined. The obtained results indicated that Ce4+ was the most effective oxidant among those tried for the polymerization of 3HT. The polymer yield was typically 29-35% without the addition of (NH4)(2)Ce(NO3)(6), but the yield improved to 53% with it. To confirm whether Fe2+ was oxidized to Fe3+ by Ce4+, a combination of Fe2+ and Ce4+ was used to perform an oxidative polymerization of 3HT. As a result, poly(3-hexylthiophene) was successfully obtained with the combination of FeCl2 and (NH4)(2)Ce(NO3)(6) as oxidative agents. This result indicates that Fe3+ was formed by the oxidation of Fe2+ with Ce4+, followed by catalytic oxidative polymerization. [GRAPHICS] .