Trimetallic FeCoNi-nitrogen/carbon nanofibers (FeCoNi-N/CNFs) were synthesized by combining electrospinning and impregnation method. The Fe/Co/NI ratio exerted great effects on their properties. When the Fe/Co/Ni ratio was 4:2:1, the sample exhibited good electrocatalytic performance for oxygen reduction reaction (ORR) in 0.5 M H2SO4, and its activity and stability were close to those of commercial 20%Pt/C catalyst. The excellent activity of this catalyst was probably attributed to the high N content, high proportion of pyridinic-N and quatemary-N, and the existence of metal nitrides. Especially, the metal nitride of Fe2N existing in the FeCoNi-N/CNFs with a Fe/Co/NI ratio of 4:2:1 played an important role during ORR. This kind of trimetallic nanomaterials is of great potential in fuel cells.