A novel FCC process for maximizing iso-paraffins (MIP) has been developed by Research Institute of Petroleum Processing, SINOPEC. The MIP process is capable of reducing olefin content and increasing iso-paraffin content of gasoline to meet the new specification of gasoline of olefin content less than 35 vol.%. The MIP reactor is a combination of a conventional FCC riser (section I) and a dense circulating fluidized bed (section II), acting as two different reaction zones, respectively. This paper is devoted to improving the understanding of gas-solids flow patterns in the MIP riser. Experiments were conducted in a 10.2 in high two-stage riser with diameters of 45 turn in lower section and 90 mm in upper section. FCC catalysts were carried by atmospheric air in the experiments. The overall and local flow patterns were determined by using the axial pressure profiles measurements and radial local optic fiber probe measurements of particles velocity and voidage at different riser height. The measurements revealed that a much complex axial and radial profiles of voidage and particle velocity existed in the riser. Significant velocity fluctuations and a much lower voidage existed at the inlet of section II due to the influences of diffuser and particles feeding above the diffuser. The influences of gas velocity and additional particles feeding on the pressure drop and solids circulating rate were different in section I and in section II. In section II, these influences weakened with the height increased. (c) 2005 Elsevier B.V All rights reserved.