Kinetics of thermally induced damage of rat liver at different constant temperature (55～95℃) were studied with continuous wave transillumination technique. It showed that thermal damage could be described by scattering coefficient. According to the relation of change in scattering coefficient and time at different temperature, the activation energy (E=135 2 (kJ/mol)) and entropy of activation  (Δ S=116 7 (J/K·mol)) were calculated. The thermal damage of rat liver was analyzed. This work provides a new method to measure thermal damage properties.