Poly(3-octyl-thiophene) (POT) and polypyrrole (PPy) iron oxalate composites were synthesized through a post-polymerization oxidative treatment. The composite of the latter has been prepared also by electrochemical polymerization. The samples have been characterized by X-ray diffraction (XRD), impedance spectroscopy, scanning electron microscope (SEM) combined with energy dispersive X-ray (EDX) spectroscopy, Mossbauer spectroscopy, cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). In case of PPy, two peaks in the XRD spectra show the presence of iron containing composite, while with POT only the layered structure originating from the octyl side-chain interactions was modified by the composite formation. The assumption of the weakening of short- and long-range interactions was proven by the decrease in conductivity of the composite. The successful electrochemical synthesis resulted a composite of similar to 5% iron content, determined by EDX. Mossbauer spectroscopy measurements evidenced a composite containing mixed valence iron oxalate doping ions, which supports the indirect EQCM data. (C) 2007 Elsevier Ltd. All rights reserved.