N-doped carbon materials are discussed as catalyst supports for the electrochemical oxygen reduction reaction (ORR) in fuel cells. This paper deals with the preparation of Pt nanoparticles (NPs) supported on N-doped carbon nanofibers (N-CNF) from a polyaniline nanofiber (PANI NF) precursor, and investigates the ORR activity of the produced materials. Initially, Pt NPs are deposited on PANI NFs. The PANI NF precursors are characterized by near edge X-ray absorption fine structure (NEXAFS) and transmission electron microscopy (TEM) measurements. It is shown, that in the PANI NF precursor materials electrons from the Pt are being transferred towards the π-conjugated systems of the aromatic ring. This strong interaction of Pt atoms with PANI explains the high dispersion of Pt NPs on the PANI NF. Subsequently, the PANI NFs precursors are carbonized at different heat-treatment conditions resulting in structurally different N-CNFs which are characterized by NEXAFS, X-ray photoelectron spectroscopy (XPS) and TEM measurements. It is shown that an interaction between N-groups and Pt NPs exist in all investigated N-CNFs. However, the N-CNFs differ in the composition of the N-species and the Pt-NPs. A small mean Pt NPs sizes with a narrow size distribution is attributed to the presence of pyrdinic N-groups in the N-CNFs. Whereas, for the N-CNFs with mainly graphitic and pyrrolic N-groups an increase in the average Pt NP size with a broad size distribution is found. The ORR activity in alkaline media investigated by Koutecky-Levich analysis of rotating disk electrode measurements showed a largely enhanced ORR activity in comparison to a conventional Pt/C catalyst.