Liquid axial dispersion and gas hydrodynamics were studied in water-air bubble column under slug flow conditions. Two models were presented, compared and discussed in order to describe the liquid axial dispersion with analytical solutions. A bubble column with diameter of 7.6 cm and length of 63 cm was used in this study. The column was equipped with concentric distributor that consisted of perforated plate and nozzle. The column design, distributor type, and operating conditions were selected to ensure slug flow regime. A novel technique with step injection of tracer material was implemented to determine the axial dispersion coefficient. New correlations were presented for gas holdup and liquid axial dispersion coefficient as functions of gas and liquid superficial velocities under slug flow conditions. In contrast to results reported by other investigators, this study showed that the liquid superficial velocity had negligible effect on gas holdup, but had significant effect on the axial dispersion coefficient. In addition, results of this study can be used to characterize liquid axial dispersion in bubble columns based on simple and direct measurements. (C) 2002 Elsevier Science B.V. All rights reserved.