Nanostructured transition metal carbides (TMCs) with superior electrochemical properties are promising materials for high-efficiency energy-storage applications. Herein one-dimensional molybdenum carbide nanofibers (Mo2C NFs) have been fabricated by a facile and effective electrospinning strategy. Based on the cross-linked network architecture with ultrahigh electronic conductivity, each Mo2C NF is uniformly encapsulated in lamellar manganese dioxide (MnO2) via electro-deposition, forming a self-supported MnO2-Mo2C NF film with excellent electrochemical activity. Remarkably, the highly conductive inner layer of porous Mo2C NFs acts like a "highway" to facilitate charge transport and ionic diffusion, while the MnO2 nanosheets with abundant active area are favorable for the accumulation of effective electric charges. Benefiting from these features, the hybrid film is directly applied as the self-standing electrode of supercapacitors (SCs) without any additives, which delivers considerably large specific capacitance with strong durability in both aqueous and organic (ionic liquid) electrolytes. This work elucidates a feasible way toward heteronanofiber engineering of TMCs on a promising additive-free electrode for flexible and high-performance SCs.