The effect of agitation on the fluidization performance of a gas-solid fluidized bed with a frame impeller is experimentally and numerically investigated. A 3-D unsteady computational fluid dynamics method is used, combining a two-fluid model and the kinetic theory of granular flow. The rotation of the impeller is implemented with a multiple reference frame method. The numerical model is validated using experimental data of the bed pressure drop and pressure fluctuation. Although the minimum fluidizing velocity and bed pressure drop are independent of the impeller agitation, a sufficiently high agitation speed yields higher fluidization performance with reduced bubble diameters and internal circulations of particles. The fluidized bed can be divided into three zones: inlet zone where the gas distribution plays a major role, agitated fluidization zone where the impeller agitation has a positive effect on fluidization, and free fluidization zone where the impeller agitation has no effect on fluidization. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 1066-1074, 2013