The present invention relates to a cathode for an electron gun for increasing its life cycle under a high current density load by ensuring a diffusion path of reducing component served for generating free radical barium. The present invention discloses a cathode for an electron gun comprising a base metal composed of nickel and at least one kind of reducing component, an upper metal layer formed by spraying powder to the surface of the base metal, implanting Ni thereto, or grinding the surface thereof and heating it, and an electron emitting layer containing alkaline earth metal oxide including at least barium on the upper metal layer.