With methyl methacrylate as monomer, 2,2’-azobisisobutyronitrile as initiator, poly(N-vinylpyrrolidone) as stabilizer and sodium styrene sulfonate as ionic monomer, a type of poly (methyl methacrylate) (PMMA) microsphere with the average particle size range from 0.5 μm to 0.9 μm were prepared by dispersion polymerization in the ethanol/water mixture medium. The effects of various parameters on particle size and distribution of microspheres were investigated. The results show that the mass fraction of monomer, ionic monomer and dispersant have obvious effects on PMMA particle size and distribution. The size scale of PMMA microspheres increases with increasing the mass fraction of monomer or decreasing the dosage of the ionic monomer and dispersant, whilst the size distribution of microspheres becomes broad. With the addition of ionic monomer into the initial reaction system, the stability of polymerization procedure shows a great improvement, and the microspheres show a clear spherical morphology, no conglutination or agglomeration of microspheres can be observed. Most importantly, the dosage of dispersant is dramatically reduced. The desired monodisperse PMMA microspheres are obtained successfully only using 3% dispersant when the mass fraction of monomer, initiator, ionic monomer is 11%, 1.0%, and 0.2%, respectively, with the volume ratio of ethanol/water in a range of 0.8 to 1.0.