A novel electrochemical sensor was prepared for detecting nitric oxide (NO) in biological materials using aligned ruthenium oxide nanowires deposited on a Pt filament by chemical vapor deposition (CVD) in two steps. First, ruthenium carbonyl (Ru 3(CO) 12) was thermally decomposed in a quartz tube furnace, and a thin film of ruthenium oxide was allowed to condense on the inner wall of the tube in a peripheral region of the furnace. In the second step, the ruthenium film was oxidized at a higher temperature and allowed to diffuse away from the center of the furnace and to precipitate on the surface of a silicon wafer or Pt filament. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) of the coated silicon wafer revealed that the product consisted of aligned ruthenium oxide (RuO 2) nanowires. The nanowire-coated Pt filament was utilized as an amperometric electrochemical sensor to detect nitric oxide gas in the aqueous phase. This sensor had much higher sensitivity (specific current) to nitric oxide than bare Pt, and the detection limit was less than 1 nM. It is anticipated that this novel sensor can be used to make biological measurements in vivo.