Bubble characteristics have been investigated in a three-phase circulating fluidized bed of 0.102 m I.D. and 3.5 m height. Effects of gas(0.01-0.07 m/s) and liquid velocities(0-0.31 m/s) and solid circulating rates(2-8 kg/m(2)s) on the bubble characteristics such as rising velocity, chord length and frequency have been determined. Probability density of bubble chord length has been examined with the variations of experimental conditions to analyze the bubble characteristics in the solid circulating regime. As a result of this study, The bubble rising velocity and frequency have increased with increasing gas and liquid velocities, but the former has decreased while the latter has increased slightly, with increasing solid circulating rates. The bubble chord length has increased with increasing gas velocity but it has decreased with liquid velocity and solid circulating rate in the riser of three-phase circulating fluidized beds. The probability density of bubble chord length becomes more narrow representing more uniform bubble size distribution with increasing liquid velocity as well as solid circulating rate in the beds. The rising velocity, chord length and frequency of bubbles have been well correlated in terms of operating variables.