Radial flow structure was studied using a fiber-optical probe in a 7.6 cm ID and 3.0 m high liquid-solids circulating fluidized bed (LSCFB). Radial solids holdup profiles were obtained at four different heights for glass beads and plastic beads of mean diameters 508 and 526 mum, respectively. The results show that local suspension densities are greater near the wall than in the center of the riser for both types of particles, confirming the existence of the radial non-uniformity. Under the same cross-sectional average solids holdup, the radial profiles of solids holdup are the same for each type of particle system under different operating conditions, but the light particles (plastic beads) show a flatter radial profile than the relatively heavier particles (glass beads). Discussion on the solids acceleration explains why a non-uniform axial profile in the LSCFB only exists for very heavy particles and only under limited operating conditions.