Stage efficiency of a pilot plant Hanson mixer-settler extraction column with seven stages was measured by using toluene-acetone-water system. The experiments were carried out for both mass transfer directions. The effects of agitation speed, flow ratio, total throughput and solute concentration oil stage efficiency were investigated and found to be significant. The comparison of investigated column with some other type of extractors showed that the stage efficiency of this column is high, while its throughput is small. Finally an empirical correlation was proposed for prediction of stage efficiency and very good agreement between experimental data and calculated values was obtained. (C) 2008 Elsevier B.V. All rights reserved.