The inactivation kinetics of E. coli and MS2 coliphage by singlet oxygen (1O2) were investigated in a homogeneous photosensitization system using Rose Bengal (RB) and visible light illumination (the Vis/RB system). The inactivation of E. coli and MS2 in the Vis/RB system was monitored over time with variations of several parameters such as pH, light intensity, concentration of RB, and the presence of dissolved oxygen. In addition, the concentration of 1O2 generated by the Vis/RB system was quantified using furfuryl alcohol under each microbial inactivation conditions. Based on the obtained results, the degree of microbial inactivation was quantitatively correlated with 1O2 exposure using the (delayed) Chick-Watson model. The Ct (concentration-time product) values of 1O2 required for 2 log microbial inactivation were found to be 1.3×10-4 mg·min/L for E. coli and 1.9×10-5 mg·min/L for MS2, respectively. The inactivation of E. coli exhibited an initial lag phase until 0.5×10-4 mg·min/L of Ct.