This paper describes the application of ultrasound waves on hydrodynamics and mass transfer characteristics in the gas-liquid flow in a T-shape microreactor with a diameter of 800 mu m. A 1.7 MHz piezoelectric transducer (PZT) was employed to induce the vibration in this microreactor. Liquid side volumetric mass transfer coefficients were measured by physical and chemical methods of CO2 absorption into water and NaOH solution. The approach of absorption of CO2 into a 1 mol.L-1 NaOH solution was used for analysis of interfacial areas. With the help of a photography system, the fluid flow patterns inside the microreactor were analyzed. The effects of superficial liquid velocity, initial concentration of NaOH, superficial CO2 gas velocity and length of microreactor on the mass transfer rate were investigated. The comparison between sonicated and plain microreactors (microreactor with and without ultrasound) shows that the ultrasound wave irradiation has a significant effect on k(L)a and interfacial area at various operational conditions. For the microreactor length of 12 cm, ultrasound waves improved kLa and interfacial area about 21% and 22%, respectively. From this study, it can be concluded that ultrasound wave irradiation in microreactor has a great effect on the mass transfer rate. This study suggests a new enhancement technique to establish high interfacial area and kLa in microreactors. (C) 2017 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.