The photoionization with synchrotron radiation (SR), a time—of-flight mas spectrometer and the colncidenee technique are combined to measure the photoionization efficiency spectra of azobenzene (AB). With these photoionization efficiency spectra, the ionization potential of AB and the appearance potentials of the major ionic fragments were obtained. From these results and the energy relation in the dissociative photoionization process, the dissociation energies of AB and AB and the ionization potential of radical C6HsN2 were derived. The photoionization mass spectra of AB using various SR photon energy were recorded. The most possible passways of the dissociative photoionization were analyzed.