A novel method has been successfully used for the preparation of ultrafiltration (UF) membranes by direct polymerization of bicontinuous microemulsions. One of these microemulsions consisted of a polymerizable cationic surfactant of ((acryloyloxy)undecyl)trimethylammonium bromide (AUTMAB), methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), and water. The other was a zwitterionic microemulsion composed of a polymerizable surfactant of(( acryloyloxy)undecyl) dimethylammonio acetate (AUDMAA), MMA, HEMA, and water. In addition, a small amount of the cross-linker ethylene glycol dimethacrylate (EGDMA) was also included in each microemulsion polymerization for improving its UF membrane strength. The uniqueness of the microemulsion system is that all organic components can readily be copolymerized at room temperature using a redox initiator. The transparent membranes thus formed showed excellent strength and performance on the separation of different molecular weights of poly(ethylene glycol) (PEG). The pore sizes of the membranes were calculated to be within the range 1-5 nm in diameter, and they could be regulated by varying microemulsion compositions.