Many organic molecules such as phthalocyanine, porphyrin and naphthalocyanine possess good electron-donating properties due to their large easily ionized π-electron system, whereas fullerene is a good π-electron acceptor that can be readily connected with other organic molecules. Therefore, a compound consisting of an organic molecule connected to fullerene is a material that could potentially be used to fabricate a photovoltaic cell, due to its large and flexible absorption combined with electrical properties similar to those of an inorganic semiconductor. For this reason, many fullerene-based supramolecules have been proposed as potential organic photovoltaic devices, and their electrochemical and photo-electrochemical properties have been measured under light illumination. We investigated the geometric and electronic structure of an organic molecule - fullerene supramolecule using an ab initio quantum mechanical calculation. The results suggest that the LUMO state of this supramolecule localized on the fullerene and that the HOMO state is localized on the organic half of the molecule.