The thermal shrinkage of Li, Na, K, Cs, ammonium, H, and Ca forms of zeolite A has been investigated by dilatometry up to 650 degrees C. The shrinkages of Li, Na, K, Cs and Ca forms are attributed to the dehydration and partial structural collapse which predominates over the normal thermal expansion and cation migration from one site to another in the zeolitic structure. The ammonium form shows a noticeable shrinkage and a possible catalytic action of the acid sites produced in the zeolite A in the combustion of ammonia evolved upon heating. The H form undergoes collapse at temperatures higher than 350-400 degrees C depending on the heating rate.