The mixing process of highly viscous liquids in a small stirred tank for High Throughput Experimentation (HTE) apparatus was investigated using a visualization approach, i.e., the Planar Laser-Induced Fluorescence (PLIF) technique. Segregated regions were detected despite a long period of agitation, indicating that the mixing homogeneity can be hardly attained for the mixing of highly viscous liquid. Based on the image analysis of PLIF results, we defined a desegregating time to quantify the mixing process of viscous liquids and to compare the mixing performances under different operating conditions. Eccentric agitation proved to be an efficient way to intensify the mixing of viscous liquid for the fact of significantly reduced desegregating time under the same stirring rate. (C) 2013 Elsevier B.V. All rights reserved.