We have studied the electron emission characteristics of tetrahedral amorphous carbon (ta-C) films with different nitrogen content. With increasing N content in ta-C, the room-temperature conductivity as well as the emission current decreases and then increases, resulting in minima. The Fermi level shifts toward the conduction band and, thus, the work function decreases by N doping in ta-C, however, the emission currents of doped ta-C films are less than those of undoped ta-C.