We prepare electrospun nanofibers (NFs) from a poly(N-vinylpyrrolidone)/manganese (II) acetate composite by electrospinning for application in supercapacitors. As-spun hybrid NFs are calcined at different temperatures to remove the polymer matrix, resulting in inorganic MnOx NFs of variable compositional ratios of Mn3O4 to Mn2O3. Interestingly, the sample of MnOx NFs that is calcined at 500 degrees C exhibits the highest electrochemical performance, reaching a high specific capacitance of 360.7 F g(-1) at a current density of 1 A g(-1). This remarkable performance is attributed to the unique three-dimensional morphology and the reduced interfacial resistance of the mixed-phase MnOx NFs within the matrix electrode and the electrolyte. (C) 2014 Elsevier B.V. All rights reserved.