We have succeeded in synthesizing Co3O4 nanosheets, nanobelts, and nanocubes with a hydrothermal process of cobalt hydroxide precursor and subsequent direct thermal decomposition. The predominantly exposed planes are {112}, {011}, and {001}, respectively. The methane combustion catalytic activity order of crystal planes follows {112} > {011} ≫ {001}. The selective synthesis of transition metal oxides with uniform and different reactive crystal planes under nanoscale conditions is expected to bring up new opportunities for design, tuning, and control of chemical activity, specificity, and selectivity.