A micro-sieve array device with dual-sized pores was designed for improving the operational flexibility and mass transfer performance of liquid-liquid extraction process at high phase ratio. The two-phase flow and mass transfer characteristics in this device were investigated and compared with the devices with mono-sized pores. In the device with dual-sized pores, well-arrangement of the large pores was available for optimizing the radial distribution of the trans-pore fluxes and weakening the immersion of the downstream pores by the upstream dispersed fluid. The optimum operation condition can thus be expanded to lower or larger trans-pore flux. The results show that an overall volume mass transfer coefficient in this device at an extreme phase ratio can range from 0.025 to 3.9 s(-1), approximately 2 magnitudes larger than that in the conventional extraction columns. The work may provide a helpful reference for the application of microdevices in large scale production processes. (C) 2012 Elsevier B.V. All rights reserved.