Abstract: Mechanically agitated tank/reactors are widely used in many industries.Mixing time is one of the key parameters for the design and scale-up of stirred tank/reactors.The mixing times in a stirred tank of 0.476 m diameter with single and multiple impellers were reported.For the single impeller agitators,the mixing times are almost the same for the different types of radial and axial flow impellers under the same specific power input.For the multiple hydrofoil impeller agitators,the mixing times of triple narrow-blade hydrofoil CBY impellers are almost the same as the dual and single CBY impellers.For the Rushton turbines,the mixing times increase as the number of impellers or the aspect ratio increases. The multiple CBY impeller configuration has a great shorter mixing time than that of multiple Rushton turbines.