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Preparation of reliable, stable, and highly responsive gas-sensing devices for the detection of acetone has been considered to be a key issue for the development of accurate disease diagnosis systems via exhaled breath. In this paper, novel CeO 2 nanodot-decorated WO 3 nanowires are successfully synthesized through a sequential hydrothermal and thermolysis process. Such CeO 2 nanodot-decorated WO 3 nanowires exhibited a remarkable enhancement in acetone-sensing performance based on a miniaturized micro-electromechanical system device, which affords high response ( S = 1.30-500 ppb, 1.62-2.5 ppm), low detection limit (500 ppb), and superior selectivity toward acetone. The improved performance of the acetone sensor is likely to be originated from the fast carrier transportation of WO 3 nanowires, the formation of WO 3 -CeO 2 heterojunctions, and the existence of large amounts of oxygen vacancies in CeO 2 . The improved reaction thermodynamics and sensing mechanisms have also been revealed by the specific band alignment and X-ray photoelectron spectroscopy analysis.