A nanofibrous MnNi/CNF (carbon nanofiber) composite electrocatalyst with diameter of 50-200 nm was synthesized via electrospinning technique and followed by a carbonization process using polyacrylonitrile (PAN), manganese acetate and nickel acetate as raw materials. XRD analysis indicated that the manganese and nickel in the composite were presented as MnO and metallic Ni respectively. The oxygen electrode using the prepared MnNi/CNF catalyst showed high electrochemical performance due to its special microstructure as mesoporous carbon nanofibers embedded with 10-20 nm particles of MnO-Ni catalyst. TEM observation and BET analysis indicated that the MnNi/CNF nanofibers possessed larger specific surface area and larger mesopore size than that of pure carbon nanofibers apparently due to the effects of the metal components on the rapid gas release during polymer carbonization. The mesoporous nanofiber structure benefited the heterophase reaction on the oxygen electrode. In addition, the presence of Ni in the nanofibers improved the electrical conductivity of the composite catalyst thus benefited the cycling and rate performances of the Li/O-2 cell. (C) 2013 The Electrochemical Society. All rights reserved.