The chemical applications of ultrasound, “sonochemistry”, have become an exciting new field of research during the past decade. Scientists now know that the chemical effects of ultrasound are diverse and include substantial improvements in both stoichiometric and catalytic chemical reactions. In some cases, ultrasonic irradiation can increase reactivities by nearly a million fold. The chemical effects of ultrasound fall into homogeneous sonochemistry of liquids, heterogeneous sonochemistry of liquid-liquid or liquid-solid systems. In this paper, some recent applications of ultrasound in organic synthesis, such as, Knoevenagel condensation, Claisen-Schmidt condensation, Michael addition, Pinacol coupling reaction, Bucherer-Bergs reaction and Biginelli reaction, are reviewed.