Suspension polymerization of styrene was performed with a forward-reverse mixing method. In the experiments, four kinds of impellers were used and it was investigated how this mixing method affected the transient size distributions of polymer droplets and the size distributions of final polymer particles. The results were compared with those obtained by conventional mixing methods. The forward-reverse mixing method was found to prevent the polymer droplets from coalescing and to produce polymer particles of the smaller and more uniform sizes than the conventional mixing methods. Moreover, the forward-reverse mixing method was able to change the particle size dramatically.