An improved type of impeller has been designed to obtain higher efficiency under the conditions of lower stirrer speed and lower gassing rate. Experiments and analyses were carried out for the absorption system of oxygen from air into water. From the experimental results, this type of impeller was found to be effective and a correlation was found between the volumetric coefficient for oxygen in the air and aeration number. For aerated agitation, it is considered that the width of impeller acts an important factor for mass transfer on agitated vessel with aeration. Some quantitative relationships were obtained between width of impeller and dimensionless groups involving a modified aeration number.