To direct highly efficient microdevice design, the mixing performance of different mixing methods was investigated. Three different microstructured mixers representing three kinds of mixing methods were utilized in this work. The mesomixing scale was adjusted through different ways in these mixers and the micromixing performance was characterized by a parallel competing reaction. A dimensionless parameter of mesomixing scale with different forms in these mixers was defined by considering contacting surface and mixing volume, and its relation with the segregation index which characterized the micromixing performance was investigated. All results indicate the enhancement of the micromixing performance with the decrease of the mesomixing scale. The mixing potential of different mixing method was discussed and it shows that the droplet cross-flow mixing method has the highest mixing potential. A linear relationship between the dimensionless parameter of mesomixing scale and the segregation index has been obtained. The results could provide much better understanding of how mesomixing scales affect the micromixing performance, which are very helpful for designing new micromixing devices and optimizing the geometric structures and operation conditions. (c) 2007 Published by Elsevier Ltd.