With the rapid development of microelectromechanical systems (MEMS) technology, heat dissipation with a high heat flux in a limited space has become a key problem restricting the efficient and stable operation of equipment. Heat-dissipation technology for liquidliquid two-phase flows in microchannels has emerged as an effective solution to this problem. This paper first reviews the classification of liquid-liquid two-phase flow patterns in microchannels. Compared with other flow patterns, slug flow is a critical flow pattern that significantly enhances the heat and mass transfer performances. This paper summarizes and analyzes the current research progress on the heat transfer of liquid-liquid two-phase slug flows in microchannels. Currently, most studies in this field rely heavily on numerical simulations, with relatively few experimental investigations. Existing numerical models often simplify the complexities of physical phenomena, and many have not been validated using experimental data. Furthermore, these models frequently employ macroscopic numerical methods such as the volume of fluid (VOF) method and finite volume method (FVM) to capture two-phase interfaces. However, the accuracy of these models when calculating the flow field, temperature field, and rates of heat and mass transfer at a twophase interface requires further verification. Experimental studies tend to focus on minichannels, primarily measuring macroscale global data such as the total pressure drop, overall heat transfer coefficient, and average fluid temperature. There is a notable lack of research involving microscale local and instantaneous data, such as the local heat transfer coefficient and detailed flow and temperature fields. Finally, future directions for the research on heat transfer for liquid-liquid two-phase slug flows in microchannels are discussed.