A small amount of mercury in process gases can destroy aluminum heat exchangers used at LNG and olefin plants. A novel process has been developed to remove the residual mercury in gas to below 0.01 mu g/m(3). It can be applied to existing plants without additional capital investment and operation costs. In the process the drying agent in the existing driers, 4A molecular sieves (4A sieves), is modified with a small quantity of silver. The Ag/4A sieves remove mercury and moisture from the gas simultaneously during the adsorption cycle. The mercury removal and dehydration capacities of Ag/4A are recovered in the regeneration cycle using the current procedure and conditions. The properties and the performance of 4A sieves for moisture removal are not affected by modification with silver. The Ag/4A sieves are active, regenerable, and stable for long term operation.