Faceted crystals with exposed highly reactive planes have attracted intensive investigations for applications. Herein, we demonstrate a general synthetic method to prepare mesocrystal Co₃O₄ with predominantly exposed {111} reactive facets by the in situ thermal decomposition from Co(OH)₂ nanoplatelets. The mesocrystal feature was identified by field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, and N₂ isotherm analyses. When applied as anode material in lithium-ion batteries, mesocrystal Co₃O₄ nanoplatelets delivered a high specific capacity and an outstanding high rate performance. The superior electrochemical performance should be ascribed to the predominantly exposed {111} active facets and highly accessible surfaces. This synthetic strategy could be extended to prepare other mesocrystal functional nanomaterials.