Fibroin nanofibrils were synthesized by a pH-controlled heat denaturation method. The nanofibrils were then applied to the surface of a carbon paste electrode to prepare a novel and biocompatible electrode for electrical double-layer supercapacitor applications. The capacity per surface area at a charge/discharge current of 1.0 A was obtained as 4.68 mF cm−2. The electrode showed improved capability and charge/discharge behavior.