Diode-like behavior was found when polyaniline (PANI) and Pt films were formed on the substrate via certain contact assembly. Micro-infrared spectrometer was used to explain the unique phenomenon that the movement of the PANI film under electrical field was the drive force for the formation of the diode-like behavior. The influence of the film thickness on the turn-on voltage and response time and the effect of the sweep step of the measurement on the turn-on voltage of the sample were carried out to further prove the above mechanism. A circuit test was given to show the potential application of such sample in the electric devices. (C) 2006 Elsevier Ltd. All rights reserved.