Chemical oxidative polymerization of 3,3-diheptyl-3,4-dihydro-2H-thieno[3,4-b] [1,4]dioxepine, (heptyl 2 -PDOT) with iron trichloride (FeCl3) gave the regiosymmetric poly(3,3-diheptyl-3,4-dihydro-2H-thieno[3,4-b] [1,4] dioxepine), poly(heptyl(2)-PDOT), which has a high glass transition temperature (195 degrees C) and a good solubility behavior in most of common solvents. Electrochemically polymerized one showed higher conductivity at the positively applied potential (1.50 x 10(-2) S/cm at +1.0 V) than the negatively applied one (2.99 x 10(-5) S/cm at -0.3 V).