Cavitational activity distribution is usually non-uniform in the sonochemical reactor and this hampers the successful design and operation of large scale sonochemical reactors. Theoretical prediction of the cavitational activity can aid in easy optimization of geometry and operating parameters as it replaces use of rigorous and expensive experimental mapping techniques for understanding the cavitational activity distribution. In the present work, an attempt has been made to predict the cavitational activity in terms of pressure field distribution by solving the wave equation in two different geometries of sonochemical reactors. Numerical simulations have been carried out by using Comsol Multiphysics software. The results are also compared with the experimental investigations reported in the earlier literature illustrations. It has been observed that cavitational activity in the case of ultrasonic horn is concentrated only near the transducer surface and is much more non-uniform as compared to the ultrasonic bath reactor with large longitudinally vibrating transducer. Comparison with experimental results has clearly established the correctness of the theoretical simulations in predicting the cavitational activity in the sonochemical reactors and hence its importance in possible scale up and optimization strategies for large scale operation. (C) 2010 Elsevier B.V. All rights reserved.