For understanding of gas-liquid mixing characteristics in an aerated agitated vessel, knowledge of bubble size distribution is very important. In this work, bubble size distribution and interfacial area were investigated for making a comparison of a pitched blade paddle creating upward flow with the Rushton disc turbine and Scaba SRGT impeller, which are commonly recommended for gas-liquid mixing. The results indicated that the size of the bubble created by the up-pumping of the pitched blade paddle could be kept small and the enhanced interfacial area could be maintained constant until 22.2 vvm, while large bubbles increased and the interfacial area decreased with an increasing gas flow rate, 4.8-15.8 vvm, for DT and SRGT. The correlation of the Sauter mean diameter with the gas now rate Q. was derived at large gas now rates for three impellers.