Polyindole hexafluorophosphate (PIPF6) was prepared by electrooxidation supplying a potential of 0.7 V. The cyclic voltammetry suggested that the electrode reaction was irreversible, and the electropol-ymerization of indole formed radical cations. Thermogravimetric analyses of the polyindole-based systems were performed at a temperature range of 25 ∼ 800°C under a nitrogen atmosphere. From the TGA results, we concluded that most polyindole systems mainly decomposed at higher temperatures than the polyaniline-based ones. The maximum thermal decomposition rate (Rmax) for polyindole systems was unaffected by the kind of electron acceptors, but the values of the polyaniline-based materials were affected by dopants. The electrical conductivity of the PIPF6was measured in a temperature range from-150 to 25°C. The values of log a at 25°C and of Eaas calculated from an Arrhenius plot were -4.15 S/cm and 0.64 eV, respectively. Our conductivity measurements suggest that a possible conduction mechanism for the PIPF6pellet is the hopping conduction, and that the charge carriers are polarons. The ESR analysis of the PIPF6powder was performed at 25°C, and, thus, parameters of ΔHPP, g-value and spectra ratio were obtained.