We describe the X-ray Astronomy Calibration and Testing Facility of the Osservatorio Astronomico di Palermo G.S. Vaiana. The facility, including a 16 meter vacuum beam line, a 1 m diameter test chamber, a X-ray source system, X-ray detectors, an advanced data acquisition and control system and other minor tools and accessories, features characteristics of vacuum cleanliness and versatility almost unique among facilities of this size. It started operating in June 1993 and will soon be completed with further equipments to improve energy resolution and to extend its capabilities to the UV band up to wavelengths of the order of 3100 A. Possible applications are test and calibration of filters, development and calibration of detectors, reflectivity measurements, testing of small X-ray telescopes. Presently it is employed for the calibration of UV-Ion shields of the High Resolution Camera of AXAF-I.