Partial oxidation of ethylene to ethylene oxide was studied using silver catalysts deposited on a low surface area support, such as α-alumina(< 1 m²/g). The selectivity to ethylene oxide has been reported to be related to the surface area of active silver species. Thus the activity of silver catalysts was studied in view of the particles size of Ag. The catalyst prepared by water-alcohol method showed higher activity. The addition of Cs as a promoter at higher temperature was observed to increase catalytic activity of silver catalysts, presumably by increasing the surface area of active silver.