The microsensors are mainly made with the single crystal silicon which requires expensive equipments and complicated process. Here, the micro-electroforming technology is used to fabricate the microresonant gas sensor. The fabricating process of the microresonant gas sensor is proposed. A microcantilever beam resonator 900 μm long, 300 μm wide, and 10 μm thick is fabricated. The resonant frequency shift is measured when exposed to ethanol vapor. Results show that the shift in the resonant frequency is approximately proportional to the ethanol vapor concentration, and the detection accuracy to ethanol vapor with the sensor is about 1 ppm per Hz frequency shift.