Hybrid structures of carbon nanofibers (CNFs) and activated carbon (AC) have been fabricated using natural potato starch as the substrate for in situ growth of the CNFs. Iron nitrate was used as both the activation agent and the catalyst precursor. The AC was derived from potato starch and the CNFs grew from the surface of AC. The hybrid structure has a large specific surface area (approximately 1930m2 g−1) and exhibits excellent electrochemical properties as supercapacitor for electrode materials. Its capacitance reaches a peak value of 268Fg−1 with an excellent cyclical ability, which is attributed to the unique hybrid structure, large specific surface area, and the high electron conductivity of CNFs grown in situ with AC. These low cost, eco-friendly CNF/AC hybrid structures are promising for energy storage.