A simple sonochemical approach was developed for the synthesis of single-crystal Au nanoprisms with triangular or hexagonal shape, 30-40 nm planar dimension, and 6-10 nm thickness in an ethylene glycol solution. It has been shown that ethylene glycol, the surfactant poly(vinylpyrrolidone), and ultrasonic irradiation play important roles in the formation of Au nanoprisms. The subsequent aging induces the growth of Au nanoprisms, which is attributed to the existence of residual reduced Au degrees atoms and Au clusters in the solution. Further growth of An nanoprisms could be realized by adding a given amount of HAuCl4 to the irradiated and aged An nanodisk colloidal solution, which provides a simple and an effective method to synthesize Au nanoprisms with different sizes. An nanoprisms with planar sizes from 70 to 400 nm have been successfully synthesized based on this strategy.