Enzymes are immobilized on activated carbon supports at high load levels and with high stability by reacting an activated carbon support with a carbodiimide or an isoxazolium salt to form active organic radicals on the surface of the activated carbon support and thereafter treating the carbon support with an enzyme solution to immobilize the enzyme on the carbon support. The immobilization of enzymes on activated carbon provides immobilized enzymes which are easily handled and which are stabilized against denaturation by hydrogen peroxide.