Inactivation kinetics of Lactobacillus plantarum by high pressure CO2 was investigated to understand the mechanism of microbial inactivation. The inactivation rates increased with pressure, temperature and exposure time, and with decreasing pH of media. Microbial inactivation was governed essentially by penetration of CO2 into cells and its effectiveness could be improved by the enhanced transfer rate. Microbial reduction of 8 log cycles was observed within 120 min under CO2 pressure of 70 kg/cm2 at 30°C. We hypothesized that the cell death resulted from the lowered intracellular pH and damage to the cell membrane due to penetration of CO2. Pressurized CO2 treatment is a potential nonthermal technology for food preservation.