Silver catalyst was prepared with α-alumina support by the impregnation method and used to produce ethylene oxide by oxidation of ethylene with air. A continuous flow reactor system was set up to investigate the activity as well as the selectivity of the catalyst under various reaction conditions. Both the catalyst in powder form （20-40 mesh） and that in pellet form (1/4 in. in diameter) were tested. While both catalysts obtained a selectivity ranging from 60 to 70 %, the catalyst in pellet form exhibited a better performance. Within the range of experimental conditions, the production rate of ethylene oxide reached the highest value, 1.2×10^-3 mole/hr-gm catalyst, when the reaction mixture containing 7.2 mole% ethylene was supplied at a rate of 300 ml/min and the reaction temperature was maintained at 230℃. Barium added as a promoter improved the selectivity to some extent, although there resulted in a significant decrease in the total conversion of ethylene. Dispersions of silver and barium inside the catalyst particle were examined by utilizing a metallurgical microscope.