An amphiphilic lanthanide complex, (E)-1-methyl-4-(2-(4-(dihexadecylamino)phenyl)azo) pyridinium tetrakis(1-phenyl-3-methyl-4-benzoyl-5-pyrazolonato) lanthanum(III),has been synthesized. It forms a stable Langmuir monolayer him on a pure water subphase (pH 5.6, 18 degrees C) when spread from a chloroform solution. Langmuir-Blodgett (LB) films were prepared by transferring the monolayers onto hydrophilic substrates of quartz and calcium fluoride with a transfer ratio close to unity. From a second-harmonic generation measurement, the second-order molecular hyperpolarizability beta of the complex was estimated to be about 1.4 x 10(-47) C m(3) V-2, which is one of the largest values for ate-based, second-order non-linear optical materials reported so far. The infrared and variable-temperature ultraviolet spectra of the film are also reported.