Suspension polymerization of styrene was conducted to study the effect of polyvinyl alcohol, added as a stabilizer to the continuous phase, on dispersed drop size distribution. Transient drop size distributions were measured under several experimental conditions with dispersedphase volume fractions ranging from 0.1 to 0.5 and stabilizer concentrations from 0.3 to 10g/l. The experimental results show that at the early stage of the reaction, where the dispersed phase viscosity is lower than about 50 cp, drop size does not depend upon stabilizer concentration. Above this viscosity, stabilizer concentration influences on drop size. Whenever drop agglomeration occurs, drop size distribution reveals a bimodal form in which the lower drop size mode in the distribution maintains a constant drop diameter while the higher drop size mode moves toward a larger drop size. The experimental results may be accounted for by the hypothesis that the coalescence of dispersed drops above the maximum stable drop size for breakup is not effectively prevented by the stabilizer.