Abstract: Three-dimensional (3D) hierarchical Co₃O₄ microcrystal with radial dendritic morphologies was prepared through hydrothermal reactions followed by subsequent annealing treatment. Structural and morphological characterizations were performed by X-ray diffraction, scan-ning electron microscopy and transmission electron microscopy. The gas sensing properties of the as-obtained microcrystal were investigated at 110 oC, which revealed that the 3D hierarchical porous Co₃O₄ microcrystal exhibited high sensitivity to ammonia, as well as a short response time of 10 s. The response characteristic indicates that the sensor has a good stability and reversibility. Detections of toxic and flammable gases, such as ethanol, acetone and benzene were also carried out at a relative low temperature. The results indicate that such hierarchical Co₃O₄ microcrystal would be a potential material in the field of gas sensing.