The radial distribution of bubbles in fine particle fluidized beds was analyzed theoretically by proposing a population balance model that takes into account both the radial coalescence and the splitting of bubbles. The following results were obtained. 1) In the case of a dynamic equilibrium between the coalescence and the splitting of bubbles, the radial distribution of local bubble frequency is expressed as the Bessel function of the first kind of order zero, taking the maximum at the bed axis and zero at the bed wall. 2) Clusters of bubbles are formed and behave as moving bodies whose size is determined by the diameters of the bed and bubbles in large-scale fluidized beds. 3) The dependency of bubble rising velocity on bed diameter can be explained with 2) above.