Stretchable conductive inks composed of a polyurethane-based elastomer containing Ag flakes were developed for smart textile applications. The conductive inks exhibited very low electrical resistivities of 10-20 εωcm when they were cured at 120 °C. An insulative ink was also prepared to be used for cover layers of wires made of the conductive inks. Stretchable circuits were formed using the electrically conductive and insulative inks on fabrics. Biosignal monitoring from human bodies was successfully performed using the circuits on fabrics as leads during normal activities of daily life.