An apparatus for continuous sterilization of fluids in which heating-up and cooling time are negligible enabled determination of the kinetics of thermal inactivation of peroxidase for the range of temperatures $110{sim}140^{circ}C$. The enthalpy of activation was 146.4 kJ/mol; free energy of activation, 113kJ/mol; and the entropy of activation, 82.9J/mol.K. Comparisons of the experimental results with the thermal destruction time curves of microorganisms showed the possibility that the time required to inactivate peroxidase might be taken into account in evaluating thermal processes for commerciel HTST methods.