Polymethylmethacrylate (PMMA) cltrafines have been prepared applying the meth- od of emulsion dispersion. Their sizes aie determined by size analysis apparatus SA-CP3. Factors affecting particle diameter and its distribution, which include PMMA conoentration, pH value and water amount, were discussed by a series of comparaison experiments. The influential principle was found, PMMA ultafines having a median diameter of 5.71μm were obtained, the ratio of the particles whose median diameters are under 10μm is 65.%. This method can be applied to the preparation of other oil-soluble polymer ultrafines, it has the advantages of simple, quick and easy to be controlled. It is possible to make it in- dustrialized in the future.
