Deposition of Langmuir Blodgett and second order nonlinear optical properties of four naphthalocyanine derivatives were investigated by using second harmonic generation (SHG) technique. The mechanisms of nonlinearity were discussed simply. For asymmetrical naphthalocyanine, the origin of SHG was the electric dipole mechanism. For symmetrical naphthalocyanine, the origin of SHG was the magnetic dipole coupling mechanism. The maximal second order nonlinear optical susceptibility χ (2) was about 3.7×10 -8 esu for tri tert butyl cyan naphthalocyanine, which was 37 times more than that of tri tert butyl naphthalocyanine.