A water-soluble ionic polyacetylene, poly(2-ethynyl-N-pentylpyridinium iodide) [PEPPI] was prepared by the uncatalyzed polymerization of 2-ethynylpyridine by using 1-iodopentane in high yield. PEPPI-iron(III) chloride complex was prepared by the reaction of PEPPI and iron(III) chloride in DMF and its properties were characterized. The electrical conductivity of PEPPI-iron(III) chloride complex was 4.3 x 10(-4) S/cm. The photoluminescence (PL) spectra of PEPPI-iron(III) chloride complex showed that the photoluminescence peak is located at 578 nm, corresponding to a photon energy of 2.15 eV. The cyclic voltammograms of PEPPI-iron(III) chloride complex exhibited irreversible electrochemical behaviors between the doped and undoped peaks. It was found that the kinetics of the redox process of polymer is controlled by the reactant diffusion process.