Catalase was chemically modified with an end-group animated dextran derivative via a carbodiimide catalyzed reaction. The enzymatic activity of catalase was increased after glycosidation with 4 mol of polymer. This modification improved the pharmacokinetic behavior of catalase, increasing by 7.8- and 20-fold the plasma half-life times for the alpha and beta phases, and reducing by 176-fold the total clearance after intravenous administration in rats.