There is fairly extensive information about mixing time under unaerated conditions in literature. However, the mixing times under aerated conditions are relatively limited, because of the insufficient measurement methods. In this work, a novel measurement technique was developed to measure mixing time under aerated conditions with an improvement on a conductivity method, by attaching a cage to the probe in order to protect the electrodes from bubbles. The effect of the cage attached to the probe and the tracer injection system on the measured mixing time was precisely investigated and it was found that the technique proposed in this work is quite effective. By using this technique, the mixing times were measured for traditional 6-bladed Rushton turbines and a modern impeller recently proposed, that is a 6-bladed hollow blade disc.