The axial and lateral solids holdup profiles in a 2-D circulating fluidized bed (CFB) were measured with an optical fibre probe under a wide range of operating conditions. The CFB is 7.6 m in height and has a 19 x 114 mm(2) narrow cross-section riser. The results showed that the operating conditions influence the flow structure significantly and control the flow in the same manner as that in cylindrical risers. The solids had lower concentrations at the riser centre than the near wall region. Compared with data from cylindrical columns, the axial and lateral profiles of solids holdup in 2-D riser had a similar pattern in shape, but were more uniform. The geometry of the riser was found to be an important factor that affects the solids distribution due to differences in terms of the perimeter per unit cross-sectional area and the wall-to-centre distance. To some extent, the two-dimensional and three-dimensional risers are more comparable under fast fluidization conditions. Generally, the solids distributions along the axial and the lateral directions in 2-D riser were dissimilar to those in cylindrical risers, while the main differences have been discussed in the current study. (C) 2010 Elsevier Ltd. All rights reserved.