The manganese peroxidase produced by Phanerochaete chrysosporium, which catalyzes the oxidation of Mn 2+ to Mn 3+ , is easily inactivated by the hydrogen peroxide (H 2 O 2 ) presented in the reaction. We attempted to increase H 2 O 2 resistance by the conformational stabilization around the H 2 O 2 -binding pocket. Based on its structural model, engineering of oxidizable Met273 located near the pocket to a non-oxidizable Leu showed a great improvement. Furthermore, after treatment at 1 mM H 2 O 2 where the wild-type is completely inactivated, full activity can be retained by engineering the Asn81, which might have conformational changes due to the environment of the pocket, to a non-bulky and non-oxidizable Ser. ß