In recent years, the circulating fluidized bed as a reactor has experienced increasing application in industry. A circulating fluidized bed (CFB) has some unique features as a chemical reactor. The performance of the CFB reactor was investigated in a 0.25-m-dia. riser system with ozone decomposition in the reactor. Both axial and radial profiles of ozone concentration are presented, as well as overall conversions under various reaction conditions. The effects of the operating conditions on the performance of the CFB reactor were examined. The experimental results show that the performance of a circulating bed as a reactor is much nearer to that of a well-mixed system than that of a plug-flow system. The effectiveness factor of the reactor seems to decrease with increase of solids holdup in the reactor.