To increase the thermal and chemical stabilities of trypsin-proteolysis activity, trypsin was immobilized on graphene oxide nanosheets (GONSs) by a one-step diimide-activated amidation. The trypsin-immobilized GONS (1.9 mg per mg-GONS) showed significantly higher thermal and chemical stabilities than the free form. After heat treatment at 50 degrees C for 6 h, the trypsin-GONS retained 80% of its initial activity, but free trypsin retained only 4% of its initial activity.