In this contribution the transient behaviour of a stirred liquid/liquid extraction column is investigated. The mathematical model for the fluiddynamics and the mass transfer taking place in such an extractor is based on a population balance and a component mass balance for the dispersed phase as well as mass balances for the continuous phase. This set of balance equations has to be set up for each compartment of the column. The simulation results were compared with experimental data from a pilot plant scale extraction column. The equipment of the column allows on line measurements of axial profiles of the drop size distribution, the dispersed phase holdup, and the solute concentration of both, the raffinate and the extract. The research program is concerned primarily with the dynamic behaviour of the column during startup and after disturbances e.g. of the inflowing streams, the agitation intensity, and the inlet concentrations of feed and solvent. Good agreement was achieved between simulation and experiment.