Nanoparticle suspensions have been extensively applied in microfluidic processes. However, researchers paid little attention to the micromixing performance of this kind of system. In this work, the micromixing performance of nanoparticle suspensions in a micro-sieve dispersion reactor was investigated with the Villermaux/Dushman method. The effects of physical properties (density and viscosity), flow velocity and particle concentration were systematically studied by using two kinds of nanoparticles, SiO2 and BaSO4. The results presented an efficiently enhanced mixing performance by nanoparticles, especially when the segregation index X-S was larger than 10(-3). Compared to the dispersed fluid, a better mixing performance could be achieved to suspend nanoparticles in the continuous fluid. A mathematical model based on Brownian movement of nanoparticles has been established to predict micromixing performance in the micro-sieve dispersion reactor. This study may provide some valuable information for the application of nanoparticle suspensions in microreactors. (C) 2014 Elsevier B.V. All rights reserved.