This paper describes the first observation of localized electropolymerization of pyrrole and aniline on highly oriented pyrolytic graphite (HOPG) substrates under atomic force microscopy (AFM) tip-sample interactions. A scanning or oscillating AFM tip, providing the horizontal scratching force and the vertical tapping force, is essential as the driving force for the surface modification with the conducting polymer. The significant tip effect on the electropolymerization has been discussed on the basis of the electropolymerization mechanism. It has been shown that under the AFM tip interaction, the electropolymerization can be blocked on the bare HOPG substrate or enhanced on the as-polymerized film. The localized electropolymerization in selected surface areas enables the nanomodification of lines, square platforms, or hollows of polypyrrole (PPY) and polyaniline (PAN) on the substrates. The result indicates that AFM can be used as a unique tool for nanofabrication of conducting polymers.