The multiphase micro-structured devices such as microchannels have been recently taken into consideration to replace the conventional equipment in different applications. The mass transfer coefficients and the interfacial area in the multiphase microchannels are much larger than those in the conventional equipment. This paper reviews the experimental studies on mass transfer in gas-liquid and liquid-liquid microchannels. Proposed flow pattern maps are compared. The featured researches corresponding to the effects of the operating conditions and the geometry of the microchannels on mass transfer are discussed. Literature review shows that influences of geometrical parameters are not investigated as extensively as those of operating conditions and thus, vague aspects of geometrical parameters effects exist. There are inconsistencies between results of some researchers and most of these are due to using dissimilar microchannel materials, unalike dominant mechanisms at different investigated operating conditions, different approaches to change the independent variable, etc.