This paper reviews recent developments on the synthesis of noble metal nanoparticles in micro and milli fluidic devices and their catalytic application in organic flow synthesis. A variety of synthesis methods using microfluidics is presented for gold, silver, palladium, platinum, and copper nanoparticles, including the for mation in singlephase flows and multiphase flows. In the field of organic chemistry, metal nanoparticles can be used as catalysts. This can lead to remarkably improved reaction performance in terms of minimizing the reaction time and higher yields. In this context, various applica tions of those metal nanoparticles as catalysts in micro fluidic devices are highlighted at selected examples. As a new direction and operational window, nanocatalysts may be synthesized in situ in flow and directly utilized in an organic synthesis. This allows making use of highly active, yet instable catalyst species, which may only have a very short life of a few seconds -a type of flashed nano catalyst organic synthesis.