Miniemulsions of styrene and butyl acrylate with sodium dodecyl sulfate (SDS) as the surfactant and hexadecane (HDE) and cetyl alcohol (HDL) as cosurfactants were prepared under high-speed stirring or ultrasonification. Results indicate that the stability of miniemulsions produced with HDE is more stable than that with HDL, when the feeding method, in which the cosurfactant is mixed with monomers, is used. There is an optical ratio (1/4) of the surfactant to the cosurfactant for maximum stabilization of the miniemulsions. The miniemulsions prepared by ultrasonification are much more stable than those by high-speed stirring. Also, a stable miniemulsion can be prepared at lower temperature (45 degrees C) when homogenizing way of ultrasonification is used. The emulsions were of a droplet-size range common to miniemulsions and some of them exhibited long-term stabilities(3 months). When these emulsions were initiated, particle formation occurred predominantly by monomer droplet nucleation. The effects of temperature, ultrasonification time, ratio of monomers, and concentrations of surfactant, cosurfactant, and initiator on the polymerization rate, conversion, and particle size were determined. It was found that the miniemulsion copolymerization of styrene and butyl acrylate with a midial amount of a redox initiator ((NH4)(2)S2O8/NaH SO3) at lower temperature (45 degrees C) can be carried out successfully by using a suitable amount of the surfactant SDS (10 mM) and the cosurfactant HDE (40 mM), when a homogenizing way of ultrasonification is applied.