Poly(3,4-ethylenedioxythiophene) (PEDOTh) films were deposited on glassy carbon (GC) electrodes from organic electrolytes containing the monomer in a solution of acetonitrile (AN). The effect of the supporting electrolyte used during electropolymerization, on the redox behavior, surface morphology, and degree of crystallinity of the films has been investigated by FTIR, cyclic voltammetry, and scanning electron microscopy (SEM) techniques. The use of LiPF6 leads to a higher electropolymerization efficiency and an increase of electroactivity and crystallinity of the polymer. On the basis of voltammetric studies of the Nernst and Butler–Volmer equations, we concluded that BF4−, ClO4−, and PF6− anions are the mobile species during the redox process of the PEDOTh films. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012