This paper reports a microchemical chip for electrochemical measurement of ion transport at the water-oil interface during microdroplet formation in a microchannel. For the electrochemical measurement of the interface, the aqueous-organic-aqueous three-phase system was formed in the microchannels. The channel wall was needed to be hydrophobic in order to prevent the aqueous phases from unfavorable intrusion. By using this system, the charging current to the electrical double layer in single microdroplet was measured.