A cathode for an electron tube includes a layer of a electron emitting substance containing alkaline earth metal oxides containing 0.01-20.0 wt % of both a lanthanum compound and a magnesium compound or a lanthanum-magnesium compound disposed on a base metal including nickel as a major component and tungsten as a minor component. The tungsten prevents embrittlement and ensures a continuing supply of fill barium in the electron-emitting substance. The cathode enjoys full interchangeability with the conventional oxide cathode and a 15-30% longer life span.
