A wearable oxygen sensor (thickness: 84μm, width: 3mm) was constructed with. a metal weldable film, a porous membrane with electrolyte and a gas-permeable membrane coated with Pt and Ag/AgCl electrodes by micro-fabrication techniques. After evaluating the sensor characteristics, the wearable sensor was placed directly to the conjunctiva of Japanese white rabbit, thus successfully monitroing the output increase with inhaling 95% oxygen gas.