Although significant progress has been made in the development of carbon-based oxygen reduction reaction catalysts in alkaline media, it is still needed to do relevant investigation of experimental factors that could influence the electrocatalytic activity of alternative electrocatalysts. In this study, we report the effect of transition metals placed into/onto nitrogen doped carbon nanofibers on the ORR performance. We demonstrated various behaviors of oxygen reduction reaction reactivity depending on embedded transition metals. Detailed physicochemical analysis showed that different surface area and pore structure were formed according to a number of metals and these structural varieties were resulted from difference in catalytic graphitization phenomenon. (C) 2015 Elsevier B.V. All rights reserved.