HOMO-LUMO gaps of the bilayer fullerene onions were investigated. For this purpose, HOMO and LUMO energies for the isolated fullerenes were calculated using the parameterization of the tight binding method with the Harrison-Goodwin modification. Then, by the consideration of the van der Waals interaction, the thermodynamical stability of possible combinations of the fullerene molecules was verified and the unstable forms were excluded. Next, the difference of the Fermi levels of the outer and inner shells was calculated by the consideration of the hybridization of the orbitals by using the geometric parameters. The results were obtained by the combination of these calculations.