Mesoporous N-doped carbon (m-N-Carbon) nanofibers with controlled numerous surface nanocavities as efficient oxygen reduction reaction electrocatalysts have been fabricated through carbonization polyaniline (PANI) nanofibers decorated with different sizes of SiO2 nanoparticles. The prepared m-N-Carbon nanofibers possess tunable mesopores, high surface area and desired nitrogen moieties. Among these, the sample m-N-Carbon (M-900) exhibits the highest electrocatalytic performance with high onset potential (0.941), half-wave potential (0.713 V), superior catalytic stability with slightly attenuated after 20000-s continuous operation and well tolerance to methanol. The enhanced electrocatalytic activities are associated with high-nitrogen content and the rational design of mesoporous structure N-Carbon nanofibers, which are contributed to the mass/electron transfer and exposure of active sites.