This paper examines the role of physical properties (interfacial tension, the viscosity of the dispersed and continuous phase, density difference, and solubility), and process conditions (flow rate, phase ratio, and temperature) on the drop size and entrainment in a static-mixer settler setup. Two extraction systems were investigated, that is, caprolactam-toluene-water and ethylbenzene (EB)-α-methyl benzyl alcohol (MBA)-water/NaOH (pH = 12). Depending on the system, the entrainment increased by a factor of 5-7, because of a change in the physical properties induced by changing the concentration of caprolactam and MBA. Different entrainment trends were observed for the two systems with phase ratio and temperature. The differences are explained by the drop break-up mechanisms reported in literature. The phase ratio effect resulted from on one hand turbulent attenuation and increased coalescence, and on the other hand increased shear and hindered settling at high phase ratios. The temperature influence was determined by its counteracting effects on the interfacial tension and the viscosities of continuous and dispersed phases.