Mixing problems are most likely encountered and sometimes can be severe in scaling-up projects.Micro-mixing is an important aspect for fast or quasi-instantaneous reactions.Poor micro-mixing might produce more undesired by-products,leading to higher purification costs.This paper gives an extensive review and analysis of micro-mixing studies in single-and multiphase stirred tanks.The relevant experiment techniques,micro-mixing models and numerical approaches are critically reviewed and analyzed with remarks and perspectives.The reported studies on two-phase micro-mixing experiments and on the impact of the presence of the dispersed phases on turbu-lence have been limited to a narrow range of conditions.More importantly,disparities widely exist among different reports.Both Lagrangian and Eulerian models are based on oversimplified assumptions,which may lead to uncer-tainties or even unrealistic results.A heuristic model,which is from the perspective of CFD(computational fluid dynamics) and can cover the whole spectrum of scales and also focus on every sub-process,is desired in the future. Mixing problems are most likely encountered and sometimes can be severe in scaling-up projects. Micro-mixing is an important aspect for fast or quasi-instantaneous reactions. Potential micro-mixing might produce more undesired by-products, leading to higher purification costs. This paper gives an extensive review and analysis of micro-mixing studies in single-and multiphase stirred tanks.. The relevant experiment techniques, micro-mixing models and numerical approaches are critically reviewed and analyzed with remarks and perspectives.The reported studies on two-phase micro-mixing experiments and on the impact of the presence of the dispersed phases on turbu-lence have been limited to a narrow range of conditions. More importantly, disparities widely exist among different reports. But Lagrangian and Eulerian models are based on oversimplified assumptions, which may lead to uncer-tainties or even unrealistic results. A heuristic model, which is from the perspective of CFD (computational fluid dynamics) a nd can cover the whole spectrum of scales and also focus on every sub-process, is desired in the future.