A pilot plant scale hollow fiber membrane system was developed for the removal of dissolved oxygen from boiler feed water via vacuum degassing process. Feed water was introduced to the shell side; a vacuum was applied to the lumen side of the hollow fiber. The effects of water flow rate, vacuum level, and water temperature on removal efficiency of dissolved oxygen and mass transfer coefficient were investigated. The membrane fouling issue was further addressed on the membrane used on the full-scale system. The foulants were identified by SEM, ATR/FTIR, EDX and water analysis to be the organic matter with the combination of aluminum silicate. Mass transfer resistances of the fouled membrane were also theoretically calculated. Finally, two membrane cleaning methods were investigated and the air backwash method was found to be effective to clean the fouled membrane and was recommended as the regular cleaning method.