We have studied blends of poly-(3-octylthiophene) (P3OT) and graphitic nanoparticles by macroscopic transport measurements, Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Scanning Force Microscopy (SFM) techniques. Their morphology as well as their mechanical and electrical properties have been characterized on a nanometer scale as a function of the carbon nanoparticle concentration in the blend. For intermediate concentrations (5–10% wt. of carbon nanoparticles) the samples present regions of pure poly-(3-octylthiophene) and round regions of polymer and carbon nanoparticles mixture, while for higher concentrations (>15% wt.) the whole sample is composed of this mixture. The interface between both regions is studied by Electrostatic Scanning Force Microscopy as a function of the applied tip-sample voltage finding evidence for the creation of new electronic states at the heterojunction. TEM images show crystalline domains of P3OT surrounded by amorphous regions. XRD measurements show that the crystallinity of the polymer increases when carbon nanoparticle concentration increases. The potential of this blends to improve the performance of organic solar cells when used as active layer is discussed.