Abstract: Deactivation kinetics of horseradish peroxidase (HRP) in catalyzed polymerization of phenols in nonaqueous media was studied. The effects of water content and temperature on the thermostability of enzyme was investigated. Thermostability of HRP is increased in nonaqueous media due to lowwater microenvironment. As hydrogen peroxide and free radical intermediate participate in enzyme deactivation, loss of catalytic activity of HRP in phenol oxidative polymerization can be greatly accelerated. Proper choice of operation conditions can effectively lead to reduction of deactivation rate and prolong the lifetime of enzyme in usage.