We fabricated graphene modified glassy carbon (Gr/GC) electrodes to enhance the direct electron transfer (DET) of bilirubin oxidase (BOD) by casting graphene-dispersed solutions with different concentrations. With a concentration of 2 µg µL−1, a large increase was observed in the reduction current at the BOD-modified Gr/GC electrode, and the value was 74 times that of a BOD-modified GC electrode (unmodified with graphene). Moreover, with graphene modification the capacitance increase was much less than with other carbon materials including carbon black and graphite powder. These results demonstrate that a graphene nanostructure is suitable for achieving the efficient DET of BOD.