Thermal death kinetics of Escherichia coli with microwaves were studied by using a tubular flow reactor with different diameters, lengths, and flow rates. Mathematical models were presented for temperature profile development and death of the microorganisms along the reactor. A first-order kinetic expression in biomass concentration simulated the death phenomena. Temperature effects on the death rate constant were expressed with an Arrhenius expression. Numerical values of the constants of this expression were found to be considerably different in microwave pasteurization experiments from those of the experiments with a constant temperature water bath. These constants were also affected by the average velocity of the medium in the reactor. Apparent death rate constants were higher with the microwave pasteurization experiments than those of the constant temperature water bath experiments at low temperatures. The results implied that tubular flow reactors may be efficiently used, especially in low-temperature pasteurization and sterilization processes.