A tracer dye technique was used to investigate the effect of the co-reverse rotational of impeller method, the agitation speed and periodic time interval on the coalescence rate in the suspension polymerization of styrene. The results showed that the extent of coalescence decreased with the use of the co-reverse rotational method and with the decrease in the periodic time interval or agitation speed. The results also showed that the final particle sizes became small and the particle size distributions became uniform with the use of the co-reverse rotational method and with a decrease in the periodic time interval.