Electrodeposited polypyrrole films in Aerosol OT emulsion media (PPyAOT) have been investigated in terms of their electrochemomechanical characteristics for various tetraalkyl ammonium (TAA) chloride salts. PPyAOT film exhibited a cathodic expansive behavior during potential cycling, indicating the reversible exchange of TAA in PPyAOT. The oxidation peaks changed with the alkyl chain length while the reduction peaks were stationary. The large cathodic expansion of 4.5% was obtained in 0.2 M tetraethyl ammonium chloride solution. The unique porous morphology on PPyAOT film seems to assist the large mobility of bulky cations.