In this work, we report the simple solid-state formation of porous Co3O4 with a hexagonal sheetlike structure. The synthesis is based on controlled thermal oxidative decomposition and recrystallization of precursor Co(OH)2 hexagonal nanosheets. After thermal treatment, the hexagonal sheetlike morphology can be completely preserved, despite the fact that there is a volume contraction accompanying the process: Co(OH)2-->Co3O4. Because of the intrinsic crystal contraction, a highly porous structure of the product is simultaneously created. Importantly, when evaluated as electrode materials for lithium-ion batteries, the as-prepared porous Co3O4 nanosheets exhibit superior Li-battery performance with good cycle life and high capacity (1450 mAh g(-1)) due to their porous sheetlike structure and small size. As far as we know, the performance of the Co3O4-based anode materials for lithium batteries presented here is the best up to now. Considering the improved performance and cost-effective synthesis, the as-prepared porous Co3O4 nanosheets might be suitable as anode electrodes for next-generation lithium-ion batteries.