Electrochemical oxidation/polymerization of 3-octylthiophene requires a relatively high potential (1.4-1.6 V vs. Ag/AgCl/Cl-) obviously causing some side reactions lowering the polymer yield. Furthermore, branching and even cross-linking of the polymer chains may occur due to coupling also at the beta'-position of the thiophene ring. This may be one of the reasons why the electrochemical polymerization of 3-octylthiophene yields a polymer which is insoluble in chloroform on the contrary to the chemically synthesized polymer.Using the dimer of 3-octylthiophene the electrochemical polymerization takes place at potentials below 1.2 V and the current efficiency during polymerization is about four times higher than for the monomer case. It is, however, necessary to use a rotating electrode during polymerization to achieve a high polymer yield. The polymer obtained using the dimer is partly soluble in chloroform and data from cyclic voltammetry and impedance measurements show that the switching from neutral to oxidized (conductive) form occurs within a narrow potential range. This can be interpreted as due to a well ordered polymer structure with a narrow distribution of the length of conjugated polymer segments.