Abstract: Local holdups in gas-liquid-solid fluidized beds with small size glass beads(density of 2460 kg•m^-3)and styrene resin(density of 1264 kg•m^-3) were measured simultaneously by improved micro-conductivity probe technique with air and water as the gas and liquid under a wide range of operation conditions.It was found that for the fluidized system, the distribution of local solid holdup showed a maximum at r/R=0.75—0.85, the cross-sectional average gas holdup showed a minimum with the superficial liquid velocity.In a certain range of axial distance from the gas distributor, radial profiles of local holdups showed severe radial mal-distribution.Such radial mal-distribution of local gas holdup disappeared with increasing axial height,while the local solid holdup did not disappear apparently.