The hydrodynamic properties in the riser and standpipe, and the cyclone efficiency have been determined in a circulating fluidized bed(CFB) unit consisting of a riser(0.05 m-ID×3.8 m high), a standpipe(0.068 m-ID×2.5 m high)as a primary cyclone/bubbling fluidized bed, and a secondary cyclone. Silica gel powder(mean diameter=46㎛) was used as the bed material. The effects of gas velocity in the riser and initial solid loading on the solid circulation rate, and the solid holdups in the riser and standpipe have been determined. The effects of gas velocity in the standpipe on the efficiencies of primary and secondary cyclones have been also determined as functions of solid circulation rate and solid entrainment rate. The solid circulation rate increases with increases in the gas velocity in the riser and in initial solid loading. The efficiencies of primary cyclone decreases and that of secondary cyclone increases slightly, with an increase in the gas velocity in the standpipe.