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A composite based on PET as a matrix and a thin layer of PANI produced by chemical polymerisation of aniline in the surface layer of the PET is investigated by means of four probe conductivity method, standard and conducting AFM, DRS and EPR techniques. Conducting AFM shows that PANI forms conducting clusters. Standard AFM topographical images prove that the undoped form of the composite has a flat surface, whereas the doped one exhibits mountainous features. DRS spectra revealed that the transition from the undoped form to the doped one is accompanied with an increase of the high frequency peak associated to conductivity of the clusters leading to the appearance of two low frequency relaxation processes connected with interfacial polarization phenomena. It is found that the relaxation behaviors of the composite doped by HClO4 and HCl acids are similar. The EPR spectra obtained in both doped and undoped forms of the composite are induced by two kinds of paramagnetic centres (PC). Irrespective to the dopant, anomalous thermal behaviors of the PC spin relaxation times and susceptibilities are evidenced above 180 K. These effects are connected with changes in the electronic transport properties.