Low-cost　and　ecofriendly　porous　biocarbons　were　fabricated　from　lkonjaku　flour　via　precarbonization　and　potassium　hydroxide　(KOH)　activation.　The　obtained　biocarbon　ACK-5　derived　from　a　precarbonized　carbon/potassium　hydroxide　(KOH)　mass　ratio　of　1:5　possessed　an　ultrahigh　specific　surface　area　of　1403　10　g4.1　and　hierarchical　porous　structures　with　the　existence　of　micro-　to　macropores.　When　AC(K)-S　was　employed　as　a　supercapacitor　electrode　in　6　M　KOH,　it　showed　a　high　specific　capacitance　of　216　F　g(-1)　and　excellent　cycling　stability　with　capacitance　retention　remaining　93.7%　after　5000　cycles.　Moreover,　the　ACK-5　sample　acquired　a　supramaximal　specific　capacitance　of　609　F　g(-1),　and　the　high　energy　density　of　AC(K)-5//AC(K)-5　symmetrical　cells　reached　up　to　9.2　Wh　kg(-1)　when　p-phenylenediamine　serving　as　a　redox　electrolyte　was　added　into　KOH　electrolyte.　The　reported　simple　fabrication　strategy　would　everage　a　green　biomass　precursor　for　the　preparation　of　supercapacitors.