Abstract: This paper introduces two methods of ultrasonic characterization of thin layers: longitudinal pulse-echo and Lamb waves. The principles have been explained, their advantages and applied conditions have been compared. The application of longitudinal pulse-echo is relatively simple, which can provide information of the thin layers such as the depth, ultrasonic velocity, attenuation etc. The disadvantage of this method is that the attenuation in the layered media and the surface roughness affect the experimental results greatly, the ultrasonic probe should have good performance. Lamb waves method is mainly used to characterize thin plate materials, without using very high frequency, it can measure the velocity of transverse wave and longitudinal wave, depth of the plate, and the bonding quality between plates. Lamb waves method is relatively accurate, however, the experimental results may be influenced by many factors, for example, the distance and oblique angle of the transmitting and receiving probe should be carefully controlled.