Surface changes of pure zeolites KY and FCC catalysts after calcination and steaming were studied using the conventional pyridine adsorption-DRIFTS method. The results show that (1) some adsorbed pyridine concomitantly interacts with acid sites (Lewis) and their adjacent Si-OH groups; (2) Si-OH-Al Bronsted acid sites in small cages are easier to be destroyed by steaming than those in supercages; (3) steaming produces new types of Bronsted acid sites in zeolites and FCC catalysts. Species with different origins may have similar IR absorption; (4) the new type of acid sites produced in FCC catalysts at later stages of steaming dominate catalytic cracking activity; and (5) the newly-formed Bronsted acid sites hare lower acid strength than the original ones in the zeolites.