Mixing performance at unsteady speed within a single revolution was studied. Because the location of the vortices centers varied, the centers of stagnant domains of doughnut shape that are formed in laminar flow disappeared and the mixing time decreased drastically. For conventional impellers operating in laminar flow, the unsteady speed mixing technique was found to be much more effective than the steady speed mixing. The study confirms that asymmetric impellers are very useful in laminar mixing vessels.