The sorption of Kr on three carbon molecular sieves, two activated carbons, and 5A Linde zeolite sieve has been studied at 77°, 195°, 273°, and 298°K. Except at 77°K, the carbon molecular sieve, exhibiting 5A molecular sieve properties, adsorbed more Kr than any other sample, at low relative vapor pressures at which the gas is released from nuclear reactors. With the exception of the zeolite sieve, sorption results for all samples could be satisfactorily represented by the Dubinin theory for adsorption in microporous solids. Heats of adsorption and structural parameters of the microporous adsorbents have been reported.