Co 3 O 4 nanoneedle arrays were successfully fabricated via a facile two-step approach, including the formation of needle-shaped Co(CO 3 ) 0.5 (OH)·0.11H 2 O followed by thermal conversion to mesoporous Co 3 O 4 . The Co 3 O 4 nanoneedle arrays exhibit mesoporosity and quasi-single-crystalline structure, and can directly serve as gas sensors without the conventional film formation process, owing to the directly growth on the substrates and good ohmic contact with the electrodes. The Co 3 O 4 nanoneedle arrays-based gas sensor showed high performance in ethanol detection. The highest sensitivity reached ∼89.6 for 100ppm ethanol vapor and the optimal working temperature was as low as 130°C. The high performance attributes to the unique structure of nanoneedle arrays with a variety of favorable features. More attractively, we find the special exposed crystal planes of Co 3 O 4 affect the gas-sensing properties significantly.