Liquid-liquid extraction is one of the best techniques in separation and a mixer settler is one of these separation contactors. In this research, Hanson's vertical mixer settler has been designed and built. The effects of the agitation rate, dispersed and continuous phases volumetric rates and interfacial tension on the dispersed phase hold-up in with and without mass transfer conditions have been studied. The results show that, by increasing the agitation rate and dispersed phase volumetric rate, the hold-up increases and the interfacial tension and continuous phase volumetric rate have reverse effects. The behaviors of hold-up with variations of operating parameters in conditions with and without mass transfer are similar but the values of mass transfer conditions are lower. Generally the proportionality between the hold-up and operating parameters in two above-mentioned conditions are found.