Interfaces between conducting polymer polypyrrole (PP) and transparent conductive materials such as indium tin oxide (ITO) andSnO2were investigated by x-ray photoemission spectroscopy (XPS). XPS lines ofIn 3d5/2,3/2andSn 3d5/2,3/2were observed in the XPS spectra of electrochemically reduced PP film sides of PP/ITO andPP/SnO2,respectively. The results indicate that electrochemical diffusion of substrate materials into conducting polymer films takes place by applying negative voltage to the substrate. The energy positions of the3dlines of the diffused In and Sn which are close to those of the metal oxides support the proposition that the diffused species are metal oxide ions. In the electrochemically diffused PP/ITO andPP/SnO2interfaces, XPS spectra of substrate sides exhibitIn 3dandSn 3dlines associated with satellite peaks, which indicates magnetic splitting of3dlevels or electron transfer typed shake-up. This indicates that electrochemical diffusion affects the substrate electronically. ©1997 American Institute of Physics.