Hierarchical　MnO2　sub-microspheres　were　fabricated　by　using　a　simple,　green　and　efficient　low-temperature　route.　These　sub-microspheres　were　formed　via　the　aggregation　of　ultrathin　nanosheets　with　a　thickness　of　2-4　nm.　An　electrode　made　of　hierarchical　MnO2　sub-microspheres　exhibited　a　specific　capacitance　of　120　F　g(-1)　at　a　current　density　of　0.167　A　g(-1).　For　an　asymmetric　AC//MnO2　supercapacitor,　it　exhibited　a　superior　electrochemical　stability　in　1　M　Na2SO4　aqueous　solution　with　88%　retention　of　the　initial　specific　capacitance　after　1000　cycles,　and　the　Coulombic　efficiency　was　above　97%,　indicating　good　charge-discharge　reversibility　and　electrochemical　stability.