This study presents the synthesis of mesostructured ZnO using a template replication method and the fabrication of a carbon monoxide sensor using the synthesized ZnO using the dielectrophoresis process. The mesoporous carbon, CMK-3, was employed for the template and zinc nitrite was used as the precursor for synthesizing the ordered porous ZnO. The mesostructured ZnO was analyzed using X-ray diffraction ͑XRD͒ patterns, scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and N 2 adsorption-desorption isotherms. The XRD patterns indicated that the ZnO exhibited a highly ordered structure after the template was removed. The morphology of the ZnO was randomly oriented and the structure was polycrystalline. The surface area, pore volume, and pore size of the porous ZnO were 61.3 m 2 g −1 , 0.31 cm 3 g −1 , and 5.3 nm, respectively. When CO gas was injected, the optimum sensitivities at 250°C were 12. 1, 14.6, 18.4, 26.0, and 60% when the CO concentrations were 10,20, 30, 50, and 70 ppm, respectively. Carbon monoxide ͑CO͒ is the main product from incomplete combustion processes and is toxic even at concentrations lower than 100 ppm. Its toxicity is dangerously magnified by the fact that it is colorless and odorless, and thus very difficult to detect. There has been extensive research into developing solid-state CO sensors using semiconductor oxides, solid electrolytes, and organic semiconductors. 1 Conventional solid-state sensors have been fabricated by adding noble metal elements such as Pt, Au, and Pt into the oxide semiconductors such as SnO 2 , Fe 2 O 3 , and ZnO. 2 However, few of them perform satisfactorily in terms of sensitivity and selectivity in the detection of CO.Recently, the semiconductive metal oxide gas sensors have been developed. The sensors have low cost, high sensitivity, fast response, and are compatible with silicon materials. ZnO is an interesting n-type semiconductor with a large bandgap energy of 3.4 eV at room temperature, large excitonic energy, low electron affinity, and high mechanical strength. 3 ZnO is an intriguing possibility as a sensory material due to the high mobility of its conductive electrons and its good chemical and thermal stability. Several techniques have been used to prepare ZnO sensors, including chemical vapor deposition, the sol-gel process, and evaporation. 4-6 A new method for synthesizing semiconductor metal oxide sensors was recently developed by Wagner et al. The semiconductor porous metal oxides not only have large surface areas and uniform pore dimensions, but also show a superior sensory performance to nonporous samples of the same metal oxides. 7 A good example of a solid template for porous metal oxides is mesoporous silica. In the procedure, a matrix structure is impregnated with the precursor and transformed into the porous oxide. Using mesoporous silicas for the matrix, several metal oxides have been yielded, including Co 3 O 4 , CrO 2 , and Fe 3 O 4 . 8-10 Tian et al. synthesized several porous metal oxide...