Optical second harmonic generation (SHG) from the Langmuir-Blodgett (LB) monolayer assemblies of amphiphilic porphyrin and its some metal complexes has been investigated. Distinct SHG responses were observed with monolayers of amphiphilic 5-(4-N-hexadecylpyridinium)-10,15,20-triphenylporphine bromide (free base: H2 porphyrin) and its magnesium (Mg), copper (Cu), and zinc (Zn) complexes. The efficiency of SHG was in the order of Mg → Zn → Cu → H2-porphyrins, which could be well correlated with the order of the first reduction potential of the porphyrin. The result indicated that SHG was mainly attributed to charge transfer from the porphyrin ring to the pyridinium group. The tilt angle of the molecular hyperpolarizability for the Zn porphyrin was evaluated.