The rates of enzyme catalyzed re­actions typically increase in Arrhenius fashion near the enzyme natural tem­perature, but increasing temperature eventually results in rapid decline in enzyme activity. Thermal deactivation of enzyme may involve both reversible and irreversible processes. When the temperature is kept constant.a num­ber of enzyme systems are found to be irreversibly denatured with time, of­ten following approximately a first-order decay law(l). If the heat stability of an enzyme is enhanced by immobil­ization, the potential utilization of such enzymes will be extensive(2,3). In this work the thermal deactivation rate measurements were reported for both the free and immobilized forms of cat-alase.