In the preparation of coated particles, a homogeneous distribution of the coating mass is often desired and much effort is made to obtain this. If it is possible to predict the effect of operating conditions on coating mass distributions by computer simulations, some of the experimental difficulties will be reduced. Therefore, in this study, Monte Carlo simulations of coating mass distribution of particles were performed to reproduce a series of experimental results obtained using a tumbling fluidized bed. This method was found to be applicable for reproducing the effect of the operating conditions on the coating mass distributions, showing that a more homogeneous distribution was achieved under the following conditions; long coating time, small hold up of core particles; high rate of mixing of the particles, etc. Furthermore, some predictions of the effect of operating conditions on coating mass distributions using this simulation method were performed.