The octa(nitropheny l)silsesquioxane(ONPS) -modifiedacry late emulsion is synthesized by asemi-continuous polymerization in this paper. Analysis by TEM and the particle size distribution show that the ONPS particles are homogeneously dispersed in the emulsion at a nanome terscale. Differential scanning calorimetry test shows that the addition of ONPS increases Tg of acrylate emulsion significantly, as well as the tensile strength of films, but decreases rupture elongation slightly.