Liquid-liquid two-phase flow in a mixer of mixer-settler has been studied via a computational fluid dynamics (CFD) simulation combined with the population balance model (PBM) and verified with particle image velocimetry (PIV) experiments. The simulation was performed using the multiple reference frame (MRF) approach, the Eulerian-Eulerian two-fluid model, and the standard k-epsilon model. The effects of impeller speed, flow ratio, and impeller type on flow field, droplet diameter, and dispersed phase holdup were investigated. The results showed that CFD simulation combined with PBM could predict droplet size distribution (DSD). The smaller droplets were mainly in the bottom region of the mixer, larger ones were in the top part of the mixer, and the largest droplets appeared in the impeller centre region. The DSD and holdup were more sensitive to impeller speed than to the organic/aqueous flow ratio. A dual-impeller mixer configuration was designed to enhance the mixing performance. Compared with single-impeller, the installation of dual-impellers could effectively avoid the dispersed phase dead zone above the lower impeller. When h(c) /T = 0.3, the best dispersing effect, such as uniform DSD and high mixing chamber space utilization, could be obtained.