Optical second-harmonic generation (SHG) from LB films of phthalocyanine derivative deposited on metal (aluminum: Al) and glass substrate has been investigated. In spite of the existence of the inversion center, for both Al and glass substrates, the bulk characteristic of the SHG was confirmed by the thickness dependence of the SH intensity. Drastic enhancement of the signal intensity for Pc/Al sample was also observed. In order to clarify the enhancement mechanism, the thickness-dependent SH intensity was calculated in terms of the quadrupole mechanism. As a result, it is possible that the Al layer enhances the SHG due to the quadrupole process.