In this work, the liquid-liquid catalytic phase transfer reaction between benzyl chloride with sodium sulfide was investigated in a capillary-microreactor assisted by ultrasound irradiation. A rational reaction mechanism was satisfactorily developed. The kinetics of the multiphase reaction was studied at different phase transfer catalyst concentration, sodium sulfide concentration and aqueous-to-organic phase flow rate ratio under both silent and sonication conditions. The reaction conversion was increased with an increase in the phase transfer catalyst concentration and sodium sulfide concentration under sonication conditions more profoundly than under silent conditions. Under sonication conditions, the reaction conversion was further enhanced by increasing the aqueous-to-organic phase flow rate ratio. However, under silent condition, such effect was negligible. In addition, the reaction system was studied in a mechanically stirred batch reactor under silent and sonication conditions. The reaction conversion was enhanced by increasing the agitation speed. The reaction conversion was further enhanced by the combination of mechanical agitation and ultrasound irradiation. (C) 2009 Elsevier B.V. All rights reserved.