A microfocus x-ray tube that can generate x rays with the focal spot size less than 5 mu m has been demonstrated using carbon nanotube (CNT) field emitters. A CNT cathode on a sharp tungsten tip, a magnetic solenoid lens, and a transmission-type x-ray target were adopted for the microfocus x-ray tube. The design characteristics and the operation performance of the microfocus x-ray tube are presented. Due to the small focal spot size, clear x-ray radiographic images of 6 mu m bars and x-ray images with the magnification factor of higher than 230 were obtained. (c) 2007 American Institute of Physics.