It has been widely recognized that microchannels can be used to enhance mass transfer rate between two immiscible fluids. This feature has attracted interests of many researchers in the field of chemical engineering. To exploit such feature of microchannels, the flow characteristics and mass transfer behavior must be fully understood. In addition, to construct an industrial scale process consisting of microchannels, an efficient numbering-up technique is required. In this review, an overview of the recent literature on the fluid flow and mass transfer behavior in multiphase flow in microchannels will be given. An attention is also paid to the numbering-up technique and extension to multiphase system involving three fluids.