A three-factor central composite design was adopted to investigate the effects of water flow rate, water temperature and salt concentration on electrolysis efficiency and separation efficiency of an electrolyzed oxidizing water generator. Results indicated that electric potential (7.9–15.7 V) and power consumption (16–120 W) of the electrolysis cell were not affected by water flow rate, water temperature or salt concentration in the feed solution. Electric current of the cells changed in between two levels (7.41 ± 0.1 and 7.68 ± 0.1 A) depending on water temperature and water flow rate. Electrolysis efficiency of the electrolysis cell, represented by the reduction ratio of chloride ions, varied in the range of 23–51%. Separation efficiency of the cation ion-exchange membrane, represented by the reduction ratio of sodium ions, varied in the range of 2–40%. Both efficiency rates were significantly reduced by increases in water flow rate and/or salt concentration in the feed solution.