Polymer nanocomposite dielectrics with high energy densities have shown great potential in electrical energy storage applications. However, these high energy densities are normally achieved at ultrahigh applied electric fields (>= 400 MV/m), which is inconvenient for certain applications such as aerospace power systems and microelectronics. In this study, uniform BaTiO3 nanofibers (BT nfs) with a large aspect ratio were prepared via the electrospinning method, surface modified by poly(vinyl pyrrolidone) (PVP) and utilized as the fillers in the poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) nanocomposites. It is found that the nanocomposite with 3 vol% BT nfs possesses a much enhanced discharged energy density of 8.55 J/cm(3) at an applied electric field of 300 MV/m, which is 43% higher than that of the neat polymer matrix (i.e. 5.98 J/cm(3)) and more than four times that of the commercial biaxial oriented polypropylene dielectric (2 J/cm(3) at over 600 MV/m). Comparative studies have been performed on the corresponding nanocomposites with BT nanoparticle fillers and pristine BT nfs. The improved energy storage performance is ascribed to the synergetic effects of surface modification and large aspect ratio of BT nfs. Our research provides a facile and effective approach to high-performance electrical energy storage materials which work efficiently at relatively low operating voltages.