A temperature sensor using two thermoelectric liquid electrolytes in microfluidic channels is proposed, and fabricated, and evaluated. Two different electrolytes, which Seebeck coefficients are positive and negative, are electrically connected via a metal electrode. The electrode was deposited on the backside of a heat stage, which means the electrical contact area of the two electrolytes are heated as the stage is heated. The sum of the thermoelectric voltage from the two electrolytes is observed changing the temperature of the heat stage. The sensitivity of the conventional metal thermocouples depends on the Seebeck coefficients of the composed materials; however, the absolute values of the solid materials are not so large (less than few-hundreds V/K or so). Some liquid electrolytes show the relatively large absolute value of the Seebeck coefficient; however, the liquid cannot keep their interface at the contact area because of the mixing and diffusing. A temperature sensor based on a liquid thermocouple is proposed, and the proto-type is fabricated. Moreover, the performances of the thermoelectric voltage response and temperature resolution are evaluated. As a result, the thermoelectric voltage of 10.6 mV/K and the resolution of 12.8 mK are obtained. The thermoelectric voltage is reasonable considering the Seebeck coefficient of the used electrolytes.