Potassium-ion　batteries　(KIBs)　in　organic　electrolytes　hold　great　promise　as　an　electrochemical　energy　storage　technology　owing　to　the　abundance　of　potassium,　close　redox　potential　to　lithium,　and　similar　electrochemistry　with　lithium　system.　Although　carbon　materials　have　been　studied　as　KIB　anodes,　investigations　on　KIB　cathodes　have　been　scarcely　reported.　A　comprehensive　study　on　potassium　Prussian　blue　K0.220Fe[Fe(CN)(6)](0.805)4.01H(2)O　nanoparticles　as　a　potential　cathode　material　is　for　the　first　time　reported.　The　cathode　exhibits　a　high　discharge　voltage　of　3.1-3.4　V,　a　high　reversible　capacity　of　73.2　mAh　g(-1),　and　great　cyclability　at　both　low　and　high　rates　with　a　very　small　capacity　decay　rate　of　approximate　to　0.09%　per　cycle.　Electrochemical　reaction　mechanism　analysis　identifies　the　carbon-coordinated　Fe-III/Fe-II　couple　as　redox-active　site　and　proves　structural　stability　of　the　cathode　during　charge/discharge.　Furthermore,　for　the　first　time,　a　KIB　full-cell　is　presented　by　coupling　the　nanoparticles　with　commercial　carbon　materials.　The　full-cell　delivers　a　capacity　of　68.5　mAh　g(-1)　at　100　mA　g(-1)　and　retains　93.4%　of　the　capacity　after　50　cycles.　Considering　the　low　cost　and　material　sustainability　as　well　as　the　great　electrochemical　performances,　this　work　may　pave　the　way　toward　more　studies　on　KIB　cathodes　and　trigger　future　attention　on　rechargeable　KIBs.