By utilizing a microreactor, extraction of ethyl ester of docosahexaenoic acid (DHA-Et) and eicosapentaenoic acid (EPA-Et) from an organic solution into an aqueous silver nitrate solution has been investigated. Slug flow preapared by using a T-shape microreactor was used to extract DHA-Et and EPA-Et. Utilizing slug flow created large specific interfacial area between aqueous and organic phases, and ultra fast extraction has been achieved. Extraction of both DHA-Et and EPA-Et took less than 20 s to reach equilibrium. In all of the experiments, the amount of DHA-Et or EPA-Et extracted was the same to that expected from the batch experiment. These facts indicate that the microreactor system can realize an ultra-fast examination system of extraction equilibrium. In addition, by maintaining the temperature quite low, a drastic improvement of extraction ratio is exhibited under a low silver nitrate concentration condition. That is, it can easily cut down silver nitrate by utilizing a microreactor. This is preferable for the practical operation. Copyright © 2007 The Society of Chemical Engineers, Japan.