Abstract: The invention describes a process for thermal activation of zeolites that are sensitive to hydrothermal degradation by percolating a hot gas through a homogeneous bed of granulates of the said zeolites. It applies to type A an X zeolites, and more particularly to their forms exchanged by potassium or calcium and one preferably uses air, the temperature of which ranges between about 300.degree. C. and 700.degree. C., preferably between 550.degree. C. and 600.degree. C., and preferably with dehydrated and decarbonated air, forced through the bed of granulates at linear velocities ranging between 0.01 and 1 m/second NTP. The process makes it possible to obtain novel zeolites with high nitrogen adsorption capacity.