Abstract: An experimental technique for the determination of the acoustic nonlinearity parameters of materials with Rayleigh waves excited directly is presented.Rayleigh surface waves were generated in materials by exciting at the specimen's edge with a special gated amplifier,and the propagating Rayleigh waves were measured with a laser interferometer system.After the Rayleigh wave signals were processed with FFT method,the acoustic nonlinearity parameters of materials were then determined from the absolute magnitudes of the fundamental and second harmonics of Rayleigh surface waves.This procedure was used to determine the acoustic nonlinearity parameters of aluminum alloy 2024 and 6061.It is shown that the results compare well with those available in the literature,this method thus can be used to evaluate the acoustic nonlinearity parameters of materials effectively.This technique can provide a practical way in the nondestructive characterization of the degradation of materials and structures in the early fatigue life.