Microemulsion polymerization is a new approach for preparing nanosize polymer materials. In this article, a nanosize poly(methyl methacrylate) (PMMA) was prepared by a novel microemulsion polymerization. The kinetics of the polymerization and the effects of the temperature, the monomer, and emulsifier/water ratio on the polymerization were investigated by means of the conversion, the transmittance, and the refractive index measurements. The structure of the obtained PMMA microlatex was studied through transmission electron microscopy (TEM), nuclear magnetic resonance (H-1-NMR), and differential scanning calorimetry (DSC). The results show that the polymerization exhibits typical kinetic characteristics of a microemulsion polymerization, i.e., there only exists two rate stages: a stage of increasing rate, and a stage of decreasing rate, and no constant rate stage is observed during the polymerization. The obtained PMMA microparticles are very uniform, regular, and small, being about 17-33 nm in the number-average diameter. The polymer has higher molecular weight (1.71 X 10(6) viscosity average molecular weight), higher tacticity (51% syndiotacticity), and higher glass transition temperature (127degreesC), much different from the commercial PMMA. Experimentally, a stable and transparent PMMA microlatex with higher polymer content (30-40 wt %), lower weight ratio of emulsifier to water (EfW less than or equal to 0.03) and emulsifier to monomer (E/M less than or equal to 0.05) as well as smaller particle size (d(p) < 40 nm), has been prepared, which is very important for the industrialization of the microemulsion polymerization technique.