Although　potassium　batteries　(KBs),　such　as　potassium-metal　batteries　and　potassium-ion　batteries,　promise　low　cost　and　high-energy　density,　specialized　separators　are　not　available　that　can　satisfy　the　KBs　operations.　In　this　work,　a　hierarchical　porous　cellulose　(HPC)　separator　with　high-performance,　by　engineering　of　the　natural　supra-molecular　structure　of　cellulose,　is　reported.　The　supra-molecular　and　hierarchical　structure　of　cellulose　provides　the　separator　with　high　porosity,　excellent　mechanical　properties,　superior　electrolyte　wettability,　and　stable　thermal　performance.　The　incorporation　of　small　pore　size　(0.64 µm)　and　suitable　tortuosity　(1.83)　reveal　that　the　separator　enables　uniform　current　distribution　and　inhibits　the　puncturing　of　K　dendrites.　Thus,　a　lifespan　of　more　than　1000 h　for　a　K//K　symmetric　cell　is　achieved　without　short-circuiting.　Benefiting　from　the　high　K+　transference　number　(0.69),　graphite//K　and　Prussian　blue　(PB)//K　cells　with　HPC　separators　exhibited　pre-eminent　cycling　stability　(400　and　200　cycles,　respectively)　and　high-rate　performance.　Moreover,　the　PB//graphite　full　cell　with　HPC　separator　is　shown　to　deliver　a　reversible　capacity　of　86　mAh　g−1　with　100　cycles.　This　novel　HPC　separator　provides　a　possibility　for　the　sustainable　development　of　KBs　and　other　energy　storage　systems　by　the　rational　structural　modification　of　plants.　©　2022　Wiley-VCH　GmbH.