Abstract: The open turbine rotating disc contactor (OTRDC) is a newly developed liquidliquid extraction column. In the present work, the dispersed phase holdup and flooding in OTRDC were investigated. A number of experiments were carded out in two columns of different diameters using five different liquid-liquid systems. Correlation for estimating holdup and criterion for predicting the critical rotor speed in absence of solute transfer were obtained. Furthermore, operating range of OTRDC was recognized.