Electrical properties at the nanointerfaces of head-to-tail coupled poly(3-hexylthiophene), PHT and metals (Au, Al) in sandwich type Al/PHT/Au diodes have been investigated using a nanomanipulator with the potential probing tip. It has been directly found that the highly insulating layer and the appreciable contact resistance are formed at Al/PHT with the thickness of several tens nanometer and PAT/Au, respectively. The bias dependence of the interface resistances at Al/PHT shows the origin of rectification. It has also been found that the interface resistance at PAT/Au is unexpectedly large, though the current-voltage behavior is ohmic. The results indicate the contact resistances between PHT and metals at the nanometric region are important factors to determine the diode performance. (C) 2004 Elsevier B.V. All rights reserved.