Characteristics of individual phase holdup and bed porosity were investigated in viscous three-phase inverse fluidized beds, the diameter of which was 0.152 m (ID) and the height was 2.5 m. The effects of the gas and liquid velocities, particle density (kind), and liquid viscosity on the individual phase holdups, such as gas, liquid, and solid holdups, and the bed porosity were determined. The gas holdup increased with increasing gas or liquid velocity or particle density, but decreased with increasing liquid viscosity. The value of the liquid holdup increased with increasing liquid viscosity, whereas, the effects of the gas and liquid velocities on the liquid holdup were somewhat complicated. The value of the solid holdup decreased with increasing gas or liquid velocity or liquid viscosity. The solid holdup in the beds of relatively-low-density particles exhibited a higher value than that in the beds of relatively-high-density particles. The bed porosity increased with increasing gas or liquid velocity or liquid viscosity. The values of the individual phase holdups and bed porosities correlated well in terms of the operating variables.