The adsorption of NH3, N20 and C02 gases at various temperatures on activated 5A molecular sieve has been investigated using the volumetric method and their isotherms have been determined. Using the adsorption isotherm at the normal condensation tem- perature of ammonia, the surface area of the adsorbent has been calculated with Lang- muir equation. Whether the adsorbate phase was solidated or not has been investigated with thermal analyis.