The oxygen transfer characteristics has been investigated in a designed aeration tank for oxidation treatment of pollutants. As operating variables, air flow rate(0.5-3.0 ℓ/min), rotation speed(0-1,000 rpm), number of impeller(1-3), and liquid temperature(20-40 ℃) were applied. The experimental results showed that overall mass transfer coefficient was increased with increasing air flow rate, rotation speed, and liquid temperature. Especially, air flow rate and rotation speed exhibited much distinct effect due to an increase of gas holdup and air-liquid contact area by bubble break. It was also found that overall mass transfer coefficient changes in proportion to number of impeller and the intensity of the effect is largely dependent on rotation speed. The correlational equation of overall mass transfer coefficient was obtained in terms of the operating variables such as impeller number, air flow rate, temperature, and rotation speed.