Continuous microflow synthesis is an innovative technology for chemical processes from small-scale synthesis to large-scale production. This technology enables fast and efficient mixing, rapid heating and cooling, strict temperature control, precise residence time control, and effective mass transfer. Moreover, once the reaction conditions are optimized for a small-scale operation, the same conditions are directly applicable to large-scale synthesis under the flow process. We successfully developed the alcohol dehydration process using microreactor and applied it to the large-scale production of saturated terpenoid pristane, which has been used as an adjuvant for monoclonal antibody production in mice. We then have been investigating to apply the advantageous features of the microfluidic systems to oligosaccharide synthesis. Our successful examples include α-sialylation, β-mannosylation, N-glycosylation on asparagine, α-selective glycosylation of 3-deoxy-d-manno-2-octulosonic acid (Kdo), and photo-bromination of toluene derivatives.