Little information is available regarding the effectiveness of water disinfection by CO(2) at low pressure. The aim of this study was to evaluate the use of high levels of dissolved CO(2) at 0.3-0.6 MPa for the inactivation of microorganisms. Bacteriophage T4 was chosen as the model virus and Escherichia coli was selected as the representative bacterium. The results of the study showed a highly effective log inactivation of E. coli and bacteriophage T4 at low and medium initial concentrations by high levels of dissolved CO(2) at 0.3 MPa with a treatment time of 20 min. When the pressure was increased to 0.6 MPa, inactivation of both microorganisms at high initial concentrations was improved to different extents. Neither pressurized air nor O(2) effectively inactivated both E. coli and bacteriophage T4. The pH was not a key factor affecting the inactivation process by this method. The results of scanning electron microscopy of E. coli and transmission electron microscopy of bacteriophage T4 suggested that "CO(2) uptake at high pressure and bursting of cells by depressurization" were the main reasons for lethal effect on microorganisms. This technology has potential for application in the disinfection of water, wastewater, and liquid food in the future.