Abstract: Microemulsion systems have been widely studied in the field of extraction and separation due to their advantages of large specific surface area, convenient separation and good solubilization. In the extraction process, the extractants combine with metal ions to form complexes, which further aggregate to form reversed micelles. With an increase in the concentration of metal ion, the reversed micelles might undergo a structural change or even secondary assembly. Considering that the extraction process can be also based on the designed water-in-oil(W/O) microemulsion, the extraction mechanism is divided into two types: (1) A typical extractant, which is saponified or protonated, or a conventional surfactant act as the main component constructing the W/O microemulsion to extract metal ions; (2) Together with a conventional surfactant, a typical extractant serves as the cosurfactant constructing the W/O microemulsion to extract metal ions, in which the former is the structural component and the latter the functional component. The mechanisms of the synergism and the formation of third phase in extraction have always been important scientific issues in the field of extraction chemistry. In this review, the mechanism of synergistic extraction and the formation of third phase in terms of reversed micelles and W/O microemulsions is clarified. In addition, the application of ionic liquid based microemulsions on extraction as well as several new separation techniques with microemulsions are introduced. In the end, the perspective of extraction concerning reversed micelles and W/O microemulsions is presented.