Co3O4 nanosheets (NS-Co3O4), nanorods (NR-Co3O4), and nanofibers (NF-Co3O4) were fabricated via hydrothermal and electrospinning methods, respectively. Single crystal sheet-like Co3O4 was mainly exposed of (111) planes with a specific surface area of 39.2 m(2)/g, while NR-Co3O4 and NF-Co3O4 were polycrystalline with specific surface areas of 53.1 and 67.1 m(2)/g, respectively. Gas sensing response (R (g) /R (a) ) of NS-Co3O4 to 100 ppm acetone was similar to 6.1 at 160 A degrees C, which was much higher than those of NR-Co3O4 (similar to 4.0), NF-Co3O4 (similar to 2.7) and other reported Co3O4 nanostructures. The response and recovery time of NS-Co3O4 to 100 ppm acetone were 98 and 7 s, respectively. NS-Co3O4 had the smallest specific surface area, but exhibited the best acetone sensing properties, which was possibly due to their high exposure of (111) planes. There were only Co2+ cations on (111) planes, which contained a lot of dangling bonds. Oxygen species in air could be adsorbed more easily on (111) planes than other randomly exposed planes. Thus, thicker holes accumulation layer formed and better gas sensing properties were obtained. This study has provided a basic understanding of the relationship between Co3O4 nanocrystals with exposed certain planes and their gas sensing properties.