Abstract: The properties of γ-ray-reduced graphene oxide samples (GRGOs) were compared with those of hydrazine hydrate-reduced graphene oxide (HRGO). Fourier transform infrared spectroscopy, X-ray diffractometry, Raman spectroscopy, Brunauer–Emmett–Teller surface area analysis, thermogravimetric analysis, electrometry, and cyclic voltammetry were carried out to verify the reduction process, structural changes, and defects of the samples, as well as to measure their thermal, electrical, and electrochemical properties. Irradiation with γ-rays distorted the structure of GRGOs and generated massive defects through the extensive formation of new smaller sp²-hybridized domains compared with those of HRGO. The thermal stability of GRGOs was higher than that of HRGO, indicating the highly efficient removal of thermally-labile oxygen species by γ-rays. RRGO prepared at 80 kGy showed a pseudocapacitive behavior comparable with the electrical double-layer capacitance behavior of HRGO. Interestingly, the specific capacitance of GRGO was enhanced by nearly three times compared with that of HRGO. These results reflect the advantages of radiation reduction in energy storage applications.