Microchannel reactors were designed and made from stainless steel through high-precision processing technology. The flow condition of oil and aqueous liquids in the microreactor was observed. The microchannel reactor with a settler could completely separate oil and aqueous layers at the outlet of the reactor. Extraction of Cu2+ was examined by using the reactor with the settler. Extraction properties were compared with those of conventional batchwise liquid-liquid extraction with stirring. The following results were obtained. 1) The microchannel reactor with a settler could completely separate heavy-phase and light-phase layers over a wide flow ran-e of 0.03-0.5 cm(3)/min when a syringe pump was used to feed the solutions. 2) The extraction rate of 0.01 mol Cu2+/dm(3) of the microchannel reactor with a settler was fast enough to attain extraction equilibrium within 20 second. 3) Back extraction rate of Cu2+ in the microchannel reactor was slower than by batchwise extraction operation with stirrer.