In order to control the extent of particle coating, it is necessary to clarify how the amount of coating material of each individual seed particle varies with operating condition. The influence of these conditions on the distribution of the mass of coating material, deposited on each single seed particle treated in a tumbling fluidized bed, was experimentally examined in this work. As a result, the coating mass per unit surface area of a single seed particle was proven to obey a normal distribution by number. Moreover, it also became clear that the coefficient of variation of the coating mass distribution, c(v), decreased with increasing coating time and size of the seed particle, and with decreasing their holdup. However, the rotational speed of the disk, which forces the aggregative coated particles apart, hardly affected the c(v) value in the experiment.