Nanosized cobalt oxides were synthesized by ammonia-etching of cobalt hydroxide and subsequent calcination. The effects of ammonia etching on the structures and catalytic properties of cobalt oxide were investigated. The results suggested that the cobalt oxide is composed of cubic Co3O4 having particle sizes in the range of 10-20 nm; smaller than the analogue prepared through the conventional precipitation method. Ammonia etching improved the reducibility of cobalt oxide, and facilitated the generation of surface oxygen vacancies and the production of surface-adsorbed active oxygen species. The activity of Co3O4 in propane oxidation was greatly enhanced by ammonia etching, mainly due to the smaller particle size and better redox properties. The facile ammonia-etching synthesis method has potential for large-scale and low-cost production of cobalt oxide catalyst. [GRAPHICS] .