Background and Aim: Pharmaceutical applications of natural materials from plants date back to ancient times. Oleuropein is one of the compounds that are found in olive leaves, fruit, bark and roots of Olea europaea (the olive tree) that cause the bitter taste of olive oil and fruit. The aim of this study was to develop and optimize the microfluidic device for the extraction of oleuropein into the aqueous phase using response surface methodology.Materials and Methods: In this study, a microfluidic device was used for the extraction of oleuropein from the organic extract of olive leaves into the aqueous phase. The effects of main parameters on the extraction efficiency including temperature, flow rate ratio (ethyl acetate/water) and residence time were investigated and optimized by response surface methodology (RSM).Results: The maximum extraction yield was obtained under the following conditions: deionized water as extractant phase, temperature of 40 ºC, flow rate ratio of 0.16 and residence time of 0.1010 min. The extraction yield of 70.93% was obtained under the above conditions with relative standard deviation of 2.0 %. The results of the analysis of variance indicate that unlike temperature, flow rate ratio and residence time are significant parameters. Moreover, square of temperature, flow rate ratio, residence time and interaction of flow rate ratio and residence time are significant factors. The extraction yield of the proposed microchannel was compared with conventional batch extraction method.Conclusion: The results show that the proposed technique can successfully be applied to the extract of oleuropein from the organic phase into the aqueous phase.