Emulsion polymerization with nano-scale SiO₂ particles as seeds composed of methyl methacrylate (MMA), butyl acrylate (BA), hydroxyethyl methacrylate (HEMA), and acrylic acid (AA) was studied from varying reaction temperatures, level of SiO₂ particle, HEMA, and emulsifier. The morphology of the emulsion particle was examined with a transmission electron microscope (TEM). The results showed that the addition of nano-SiO₂ particles decreased the coagulum greatly when its level was lower than 7%. The coagulum also decreased with the increasing of temperature from 65°C to 75°C. The level of HEMA and emulsifier had little influence on the coagulum in the presence of nano-SiO₂. The particle size of the emulsion increased with the increase of level of nano-SiO₂ and HEMA. Part of the emulsion particles connected together due to the existence of HEMA, and yet some of the nano-SiO₂ particles were not covered with polymer.