Double perovskite oxide Pr1-xNdxBaFe2O5+δ (PNBFx, x = 0.0–0.3) nanofiber were prepared using electrospinning and were evaluated as cathodes for solid oxide fuel cells (SOFCs). The crystalline structure, microstructure, and electrochemical performance of PNBFx were thoroughly investigated and discussed. The PNBFx nanofiber cathodes obtained after sintering at 800 °C crystallized in a tetragonal structure with the space group P4/mmm and had good chemical compatibility with SDC electrolytes at 900 °C for 4 h. Nd doping was found to increase the lattice parameter, while the average valence of praseodymium and iron content increased steadily in PNBFx. The Pr0.8Nd0.2BaFe2O5+δ (PNBF02) nanofiber cathode exhibited the best performance with a polarization resistance (Rp) of 0.072 Ω cm2 at 750 °C. When PNBF02 nanofiber was used as a single-cell cathode, the peak power density reached 1.52 W cm2 at 750 °C. All results indicate that double perovskite PNBF02 is a promising cathode material for SOFCs.