A miniaturized electrochemical-oxytocin (OXT) sensor using competitive ELISA was constructed and tested. The OXT sensor measures OXT as reduction of glucose oxidase-labeled oxytocin, which competitively captured by anti-OXT antibodies. We employed a nitrocellulose membrane as a support for antibody because the nitrocellulose membrane improved the output signal by two folds comparing with using a microtiter plate as a support. In the experiment, competitive immunoreaction was first optically measured using conventional biotinylated capture antibody and avidin-GOD. As a result, it was confirmed that oxytocin measurement was possible by the constructed immune system. After that, oxytocin was electrochemically measured on the electrode using a carbon graphite electrode. Redox currents showed a relationship with oxytocin concentration and the calibration range involved 15pg/mL, which has been reported as salivary oxytocin.