Thermal inactivation of Escherichia coli was studied under CO2 pressures of 1.2, 2.5, and 5 MPa at 25, 35, and 45°C. Two phases were observed in the destruction curves. The earlier stage was characterized by a slow rate of inactivation, which increased sharply at the later stage. An increase of pressure and/or temperature enhanced the antimicrobial effects of CO2 under pressure. The effects on cell structure were studied by scanning electron microscopy and the specific mechanism of action appeared to be related to enzyme inactivation.