A facile template-free hydrothermal method was applied to successfully synthesize a series of bulk cobalt oxides with different morphologies (1D-Co3O4 nanoneedle, 2D-Co3O4 nanoplate, and 3D-Co3O4 nanoflower). The catalytic activity for the toluene combustion over various types of catalysts was investigated. The 3D-Co3O4 nanoflower performed the excellent activity and the temperature required for achieving a toluene conversion of 90 % (T90%) at approximately 238 °C with the activity energy (Ea) of 71.6 KJ mol−1, which was 19 ℃ lower than that of 1D-Co3O4 nanoneedle with Ea of 97.1 KJ mol−1 at a space velocity (WHSV = 48, 000 mL g−1 h−1). The effect of shape on the physicochemical properties of the Co3O4 catalysts were characterized by various analytical techniques. It has been found that large specific surface area, low temperature reducibility, highly defective structure with abundant surface active oxygen species and rich Co3+ cationic species were responsible for the excellent catalytic performance of 3D-Co3O4 nanoflower. In addition, complete conversion of toluene had remained the same after 3D-Co3O4 nanoflower was observed for 120 h, suggesting it exhibited the long-term stability for toluene combustion. Therefore, 3D-Co3O4 nanoflower might be a potential non-noble catalyst in practical application.