The kinetic of thermal deactivation of CMC-ase activity of A. niger, locally isolated, was studied. The enzyme was found to be more stable in temperatures below 40 degrees C. The rates of activity decay were significant at high temperatures and can be described as a first-order kinetic model. Deactivation rate constants (Kd) were determined at different temperatures (30, 40, 55 and 65 degrees C). Kd value for CMC-ase activity decay at 65 degrees C was 28 times higher than its value at 30 degrees C. An Arrhenius type temperature dependence of Kd was found, and the activation energy (Ea) of the thermal deactivation was calculated to be 8400 cal/mole. Thermodynamic quantities (delta H) and (delta S) for deactivation process were 7700 and 11.9 cal/mole, respectively. The change of two kinetic parameters, i.e. Vmax and Km under deactivation conditions, was discussed.