Abstract: Photoionization studies of chlorobenzene were performed by using a time-of-flight mass spectrometer (TOF-MS) with vacuum ultraviolet (VUV) photons from the Heifei synchrotron radiation source. The photoionization mass spectrum and the photoionization efficiency (PIE) curves of both parent and fragment ions were measured. The appearance potentials of the major ions were obtained from their PIE curves. From these data, the standard formation enthalpies of C6H5Cl+, C6H+5 and C4H+3 were evaluated, some dissociative energy was derived. We will be able to detect chlorobenzen with SPI-TOFMS and 118.0 nm laser light.