Organic　electrode　materials　are　of　particular　interest　for　storing　large-size　potassium　ions.　Herein,　we　demonstrate　that　polyethylene　terephthalate　(PET),　a　synthetic　organic　polymer　with　functional　carbonyl　groups,　could　deliver　a　two-electron　redox　mechanism　for　potassium　storage.　The　PET　particles,　synthesized　from　PET　plastic　film　by　a　simple　solvent　thermal　method,　achieve　almost　complete　utilization　of　redox-active　sites,　providing　a　reversible　capacity　of　273　mAh/g.　Over　800　cycles　of　cycling　life　are　demonstrated　by　the　PET,　along　with　fast　K+-transport　kinetics　and　thus　outstanding　rate　performance.　Furthermore,　a　fabricated　full　cell　composed　of　PET　anode　can　provide　a　high　operating　voltage　of　3.17　V　with　a　high　energy　density　of　245　Wh/kg.　This　study　offers　a　new　way　to　utilize　PET　plastic　waste　and　guide　the　development　of　organic　anode　for　low-cost　potassium-ion　batteries.