Abstract: In this study, we were interested to study the behaviour of some molecular sieves in nitrogen gas adsorption. We were interested in first stage in the synthesis of the molecular sieves as zeolite A and faujasites X and Y. These solid crystals were the subject of a characterization by various analytical techniques such X-ray diffraction, X-ray analysis by energy dispersion and electronic scanning microscopy. The adsorption isotherms of nitrogen on these samples are obtained of type I and therefore, the Langmuir equation was verified. X and Y zeolite samples could adsorb a big amount of gas nitrogen not like that A sample witch has a small adsorption capacity. It has been also shown that the desorption speed of nitrogen is higher than that adsorption on study zeolites.