The flow multiplicity phenomenon in circulating fluidized bed (CFB) risers, i.e. under the same superficial gas velocity and solids circulation rate, the CFB risers may sometimes exhibit multiple flow structures, was numerically and experimentally investigated in this study. To investigate the flow multiplicity phenomenon, the experiments of gas-solids two-phase flows in a 2-D CFB riser with different flow profiles at the inlet of the CFB riser were conducted. Specially designed gas inlet distributors with add-ons are used to generate different flow profiles at the inlet of the CFB rise. The CFD model using Eulerian-Eulerian approach with k-epsilon turbulence model for each phase was employed to numerically analyze the flow multiplicity phenomenon. It is experimentally and numerically proved that for gas-solids two-phase flows, the flow profiles in the fullydeveloped region are dominated by the flow profiles at the inlet. The solids concentration profile is closely coupled with the velocity profile, and the inlet solids concentration and velocity profiles can largely influence the fully-developed solids concentration and velocity profiles. (C) 2011 Elsevier B.V. All rights reserved.