Recently, diverse composites between carbon nanomaterials and conducting polymers have been intensively investigated for a variety of applications such as sensors and supercapacitors. These composites have been synthesized by either chemical or electrochemical methods, which have the drawbacks of using toxic oxidants or requiring complicated apparatus, respectively. The present study reports that the graphene oxide/polypyrrole (GO/PPy) composites can be easily synthesized in a single-step catalyzed by horseradish peroxidase in an aqueous solution (pH 4.0). Scanning electron microscopy of the enzymatically synthesized GO/PPy composites shows that GO sheets are evenly coated with PPy without observable granular PPy particles. A symmetric two-electrode coin cell capacitor (20 mm in diameter and 1.6 mm in thickness) was made to measure the electrical capacitance in an aqueous electrolyte (1 mol/L NaNO3) by the galvanostatic charge/discharge method. When the discharge current was 0.5 mA, the specific capacitance of the GO/PPy composites (46.6 F/g) was similar to 390 times greater than graphene oxide (0.12 F/g) or similar to 7 times greater than polypyrrole (6.7 F/g). Furthermore, the addition of a 0.2 L/L (20 vol%) water-miscible ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), into the aqueous electrolyte enhanced the capacitance of the GO/PPy composites by 57 % at maximum.