Adsorptive removal of t-butanethiol (TBT), an odorant additive, from city gas was carried out using metal ionexchange Y type zeolites at ambient temperature and pressure. The adsorption capacity of TBT on Na _ Y under the wet gas condition was extremely low, although that under the dry gas condition was certainly higher. The adsorption capacity of TBT on silver ion-exchange Y type zeolites (Ag(Na) _ Y) increased with higher silver ionexchange ratio in Ag(Na) _ Y under wet gas condition. In contrast, the adsorption capacity of TBT on Ag(Na) _ Y under the dry gas condition decreased with higher silver ion-exchange ratio in Ag(Na) _ Y. Formation of silver sulfide clusters in Ag(Na) _ Y causes the decrease in sulfur adsorption capacity of it under the dry gas condition. The adsorption capacity of TBT on copper ion-exchange Y type zeolites (Cu(Na) _ Y) increased with higher copper ion-exchange ratio in Cu(Na) _ Y under the wet gas condition. In the case of Cu(Na) _ Y, the decrease of TBT adsorption capacity under the dry gas condition did not occur with higher copper ion-exchange ratio in Cu(Na) _ Y. The both spent samples of Ag(Na) _ Y and Cu(Na) _ Y were regenerated by heat treatment in air. The decrease in adsorption capacity of TBT on Cu(Na) _ Y was slightly lower than that on Ag(Na) _ Y.