This article reports on the measurement of the electrical properties of a single molecule, a first step for the functionalization of surfaces towards nanoelectronics applications. The study includes the preparation and characterization of monolayers of cobalt (II) porphyrin (CoOEP) self-assembled on highly oriented pyrolitic graphite (HOPG). These molecules have interesting electrical properties, form ordered and stable arrays on HOPG and can be utilized in organic electronics applications. In this work we used scanning tunnelling microscopy (STM) to obtain high resolution images of CoOEP and at the same time the respective I/V curves.