Abstract: A series of ultrastable Y zeolite samples have been prepared under various conditions. The samples show a considerable unit cell shrinkage and have a high degree of thermal stability and hydrothermal stability. The degree of crystallinity is largely over 80%. The samples also exhibit a strong acidic property involving both Bronsted acid and Lewis acid and have cracking activities comparable with LaHY zeolite. Studies of the hydrothermal stability of the acidic sites of the ultrastable Y zeolite demonstrated that 100% steam treatment at temperatures over 780℃ it eliminate almost all stronger acidic sites. Cation exchange experiment showed that Al cations formed in the stabilization step can be exchanged by NH4+.Finally the general regularities of preparation and the properties of the ultrastable Y zeolite were discussed.