A novel and highly effective UV-TiO2 photocatalytic reactor was developed for killing microorganisms, including Escherichia coli. Among tested four types of TiO2-immobilized photocatalytic supporters (glass bead, muscovite bead, alginate bead, and TiO2 thin film coated quartz tube), the muscovite bead had a 99.9% percent bactericidal activity within 5 min along with permanent longevity. Adding air bubbles or H2O2 (<50 mg l(-1)) to the sample solution significantly enhanced the killing activity in that 100% percent of bacterial cells were killed within 3 min.