Laser Doppler anemometry (LDA) was used to measure velocity, fluctuating velocity and size distribution in the riser of a circulating fluidized bed. Fluidized cracking catalyst (FCC) particles with volume average size of 70 mu m and density of 1650 kg/m(3), in a dilute gas-solid flow system with solid volume fraction ranging from 0.2% to 2.5% and solid mass flux of 10-120 kg/m(2) s were experimentally studied at the test section which was 1.07 meters away from the entrance zone. More particle collision and less slip velocity between particles of different size were observed at higher solids loadings and superficial gas velocities. At lower superficial gas velocities and lower solids loadings, instantaneous reversal flow of particles and lower particles fluctuating velocities and larger particles/agglomerates were measured along the wall. The radial distribution of axial particles velocity profile was flatter than a parabolic shape with maximum velocity of particles of different size in most cases away from the center. The particles fluctuating velocities was about 20%-30% of the particle velocity. However, it decreased at the wall region due to less probability of collision with moving particles and significant collision with the wall. In contrast, the turbulence intensity increased at the wall region due lower particles velocities in this zone.