Aqueous dispersions of lightly sulfonated polystyrene were prepared. The effects of initial polymer concentration, neutralizer, ionic content, solvent property, and store time on the stability, the particle size, and the distribution of the dispersed phase for the resultant oil-in-water emulsions were studied. It was found that the particle size varied with the variation of polymer concentration and increased with increase in the store time. The effects of the neutralizer and the mixed solvents on the particle size were also significant. The particle size increased with increase in volume of the counterion.