Nano-/micrometer　multiscale　hierarchical　structures　not　only　provide　large　surface　areas　for　surface　redox　reactions　but　also　ensure　efficient　charge　conductivity,　which　is　of　benefit　for　utilization　in　areas　of　electrochemical　energy　conversion　and　storage.　Herein,　hollow　fluffy　cages　(HFC)　of　Co3O4,　constructed　of　ultrathin　nanosheets,　were　synthesized　by　the　formation　of　Co(OH)(2)　hollow　cages　and　subsequent　calcination　at　250　degrees　C.　The　large　surface　area　(245.5　m(2)　g(-1))　of　HFC　Co3O4　annealed　at　250　degrees　C　ensures　the　efficient　interaction　between　electrolytes　and　electroactive　components　and　provides　more　active　sites　for　the　surface　redox　reactions.　The　hierarchical　structures　minimize　amount　of　the　grain　boundaries　and　facilitate　the　charge　transfer　process.　Thin　thickness　of　nanosheets　CO,　(2-3　nm)　ensures　the　highly　active　sites　for　the　surface　redox　reactions.　As　a　consequence,　HFC　Co3O4　as　the　supercapacitor　electrode　exhibits　a　superior　rate　capability,　shows　an　excellent　cydiability　of　10　000　cycles　at　10　A　g(-1),　and　delivers　large　specific　capacitances　of　948.9　and　536.8　F　g(-1)　at　1　and　40　A　g(-1),　respectively.　Catalytic　studies　of　HFC　Co3O4　for　oxygen　evolution　reaction　display　a　much　higher　turnover　frequency　of　1.67　x　10(-2)　s(-1)　in　pH　14.0　KOH　electrolyte　at　400　mV　overpotential　and　a　lower　Tafel　slope　of　70　mV　dec(-1).　HFC　Co3O4　with　the　efficient　electrochemical　activity　and　good　stability　can　remain　a　promising　candidate　for　the　electrochemical　energy　conversion　and　storage.