A sample counting cell for monitoring ultralow-level 85Kr in environmental air samples has been designed. The cell consists of ∼10 g of hydrogen mor-denite covered with 0.075-mm aluminum foil. The 85Kr is adsorbed by the hydrogen mordenite inside the counting cell. The radioactivity of 85Kr in the cell is measured by a modified external gas flow proportional counter. A refined separation method for the purification of 85Kr in the air sample has also been developed. The low detection limit for this improved counting system, including the refined separation procedure, is ∼0.02 pCi/cm3 based on 50-ℓ air samples at 1 atm. This counting method is also compared in detail with other methods.