Hydrodynamics and gas/fiquid mass transfer in fluidized beds of glass spheres (3–8 mm diameter)were studied employing viscous aqueous solutions (16–53 mPas) Increasing liquid viscosity reduced the bubble disintegration capability of the particle beds. The most pronounced consequence was a strong decrease in the volumetric mass transfer coefficients (kLa) From a comparison of kLa in Newtonian and pseudoplastic liquids it is concluded that the effective shear rates in three-phase fluidized beds are higher than in bubble columns.