A hot cathode preheating start discharge lamp comprises a lamp tube, a first electrode, a second electrode, a first heating element and a second heating element. The lamp tube has a sealed housing chamber. The first and second electrodes have respectively one end held in the housing chamber and another end connected to a power source. The first and second heating elements are spaced from the first and second electrodes without connecting therewith and have respectively another end connected to a discharge preheating controller or an electronic ballast. Thereby the invention does not need tungsten filaments or electronic powder coated on the tungsten filaments to generate a great amount of electrons like the conventional techniques do. Thus the problems of burnout and fracture of the tungsten filaments or exhaustion of electronic powder can be eliminated, and the lifespan of the lamp tube can be enhanced.