Molecular size dependence in third order optical susceptibility chi((3)) for evaporated tin-phthalocyanine thin film was examined by methods of a scanning electron microscope technique(SEM) and an optical third harmonic generation (THG) Maker-fringe technique. Evaporated molecular size influenced greatly the values of chi((3)). The thicker molecular size grew, the greater values of chi((3)) were. The values were greater with increasing the order orientation O-A = A perpendicular to/(A perpendicular to+A(II)), whose preferential direction was parallel to the major axis of microcrystals.