In this study, pyrrole-N-propionic acid (PPA) was electrochemically polymerized on a glassy carbon electrode (GCE) in various electrolytes (NaClO4, Et4NBF4, Bu4NClO4, and Bu4NPF6) using cyclic voltammetry (CV). The structure and morphology of the modified electrode was characterized by FTIR-ATR, visible-near-infrared spectroscopy (Vis-NIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The morphological characterizations of the poly(PPA) films synthesized in the various supporting electrolyte solutions were demonstrated by SEM and AFM. Electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) analysis were performed to collect information about the semiconducting properties of the poly(PPA) films. From the Mott-Schottky analysis, the carrier densities (N-D) of the poly(PPA) films obtained were 3.25x10(16),1.59x10(16), 1.17x10(16), and 0.52x10(16) cm(-3), and the flat-band potentials were 0.41, 0.32, 0.37, and 0.36 V for the poly(PPA)films in NaClO4, Et4NBF4, Bu4NClO4, Bu4NPF6, respectively. The resulting Mott-Schottky plots of the poly(PPA) films indicate that the films are p-type semiconductors. EIS analysis were performed to determine the capacitive behaviors by variation of electrolyte types in a monomer-free solution. An equivalent-circuit model of R(W(CR)(QR))(CR) was used to fit the theoretical and experimental data to interpret the polymer electrode/electrolyte interface properties and to provide information about equivalent circuit parameters.