The X-ray tube is a key component of an X-ray source. An X-ray tube used for a compact nanosecond pulsed X-ray source is described in this paper. The X-ray tube is a sealed transmission target X-ray diode. Its cathode is acomb structure formed from thin tungsten sheets with thickness of 50 μm, while its target is made of a 100 μm-thick titanium film. The X-ray dose at a distance of 20 cm from the diode is 20 mR per pulse while the diode voltage is 512 kV. In this case, the full width at half maximum of the X-ray pulse is about 5 ns.