Background and Objective: Arsenic (As) is a highly toxic metalloid found in ground and surface waters. Arsenic contamination in drinking water leads to harmful effects on human health. In this study, the efficacy of Reverse Osmosis (RO) membrane technology was evaluated for arsenic removal from drinking water. Materials and Methods: This experimental study was carried out on RO membrane spiral- wound module (model: 2521 TE, CSM Co. Korea) in pilot scale. After preparation of sodium arsenate solution in the laboratory, performance of RO membrane system in arsenic (As) removal was investigated. Experiments were conducted with five different pressures (100, 130, 160, 190, 210 Psi), pH (4, 5.5, 7, 8.5, 10), temperature (20, 25, 30, 35, 40°C) and an initial As concentration of 0.2 mg/L. The influence of different feed concentrations (0.2, 0.5, 1, 1.5, 2 mg/L) on As removal efficiency was also examined. In each step, flux was measured and after 30 minutes samples were taken. Arsenic amount in feed and permeate were measured by silver diethyldithiocarbamate (AgDDTC) method. Results: The results of this study demonstrated that greater than 90% of As can be eliminated from drinking water. Also the results showed that the pressure of 190 psi, As concentration of 0.2-0.5mg/L, temperature of 25-300C and pH = 6-8 were the optimal conditions. Conclusion: Arsenic removal efficiency in optimal conditions of system performance was up to 99%.