The barium hexaaluminate (BHA) supported Co3O4 catalysts (XCo/BHA) with varied mass loading of Co (X = 10%, 20%, 30%, 35% and 40%) were prepared by impregnating Co3O4 nanoparticles (NPs) onto BHA support that synthesized through urea combustion method. The catalyst was characterized by high-resolution transmission electron microscope (HRTEM), temperature programmed reduction (TPR), temperature programmed desorption (TPD) and valued the ammonia decomposition performance by fixed-bed reactor. The results showed that Co3O4 NPs were dispersed densely on the BHA surface, with the strong alkaline support that could adjust the binding energy of the active sites and the nitrogen, which was conducive to the ammonia decomposition reaction. Among the synthesized catalysts, 35Co/BHA achieves 87.2% ammonia conversion at 500 °C with a space velocity of 30000 ml gcat−1 h−1, corresponding to a hydrogen production rate of 29.2 mmol H2 gcat−1 min−1, and also shows excellent catalytic stability. Display omitted •BHA supported Co3O4 is highly active toward ammonia decomposition.•35Co/BHA presents the optimal ammonia conversion rate.•BHA acts as electron donor to promote ammonia decomposition.•Co3O4 NPs are densely dispersed on BHA with increased pore volume.