The structural features of the LB films of substituted fullerence C60-Be were investigated by π-A isotherm, small angle X-ray diffraction (SAXD) and optical measurements. We found that pure C60-Be molecules existed at the air-water interface in a bulk phase. NC was used as an inert material to construct mixed C60-Be/NC LB films which had a much better qulity than the pure C60-Be LB films. Our π-A, UV-visible absorption and SAXD measurements showed that the structural improvement in the mixed C60-Be/NC LB films was realized by insertion of the C60-Be molecules between the two hydrophobic chains of the NC molecules. The relatively large third-order nonlinear susceptivility χ(3)＝2.1×10-11 esu was deduced by measuring THG from mixed C60-Be/NC LB films. The NC molecules have attractive features as an inert material in fabrication of LB multilayers made from optically nonlinear materials with hydrophobic long tails or ball-like structures.