An electron emission source including a carbon-based material coated with metal carbide in the surface coating layer, of which the metal has a negative Gibbs free energy when forming the metal carbide at 1,500 K or lower, a method of preparing electron emission sources, and an electron emission device including the electron emission source. The electron emission source includes a carbon nanotube coated with metal carbide or a carbon nanotube having a metal carbide layer and a metal coating layer, which are sequentially formed thereon. Thus, the electron emission source has long lifespan without deterioration of electron emitting characteristics. The electron emission source can be used to manufacture electron emission devices with improved reliability.