The Graesser liquid-liquid contactor is attractive for processing aqueous two-phase systems because of gentle agitation and low throughput characteristics. In this study, axial mixing and flooding characteristics of a Graesser contactor (100cm × 10cm ID) were studied using an aqueous two-phase system comprising polyethylene glycol 1500 Da and potassium phosphate at pH 7 and 25°C. The influences of the operational variables rotor speed and flow rate ratio on the axial mixing were analyzed. We observed increasing axial mixing with increase of the polymeric phase superficial velocity. The axial mixing coefficient showed an increase at greater rotation speed. The flooding flow rates at 6.6 rpm were 80 mL min-1 for the saline phase and 8 mL min-1 for the polymeric phase. © 2004 Elsevier B.V. All rights reserved.