Synthesizing　CHA-type　zeolite　via　template-free　interzeolite　transformation　has　been　considered　as　a　green　method,　but　the　resultant　zeolite　exhibits　low　activity　in　the　selective　catalytic　reduction　of　NOx　by　ammonia　(NH3-SCR).　Herein　we　report　a　highly　active　NH3-SCR　catalyst　(Cu-CHAUSY)　derived　from　CHA-type　zeolite　(CHAUSY)　that　is　synthesized　via　template-free　interzeolite　transformation　from　ultra-stable　Y　(USY).　The　ultra-high　activity　is　attributed　to　the　specific　silicon　and　aluminum　configurations　in　USY　which　are　distinctly　different　from　those　in　the　conventionally　used　parent　NaY,　although　they　have　similar　SiO2/Al2O3　ratios.　This　characteristic　endows　CHAUSY　with　more　single　Al　atoms　in　a　six-membered　ring,　benefiting　the　self-reduction　of　[Cu(OH)]+　and　the　activation　of　O2　during　the　NH3-SCR　reaction.　Moreover,　Cu-CHAUSY　is　demonstrated　to　outperform　the　two　reference　catalysts　prepared　from　the　aluminosilicate　gel　by　conventional　hydrothermal　crystallization　with　the　assistance　of　organic　templates.　Our　work　provides　a　new　strategy　for　preparing　highly　active　NH3-SCR　catalysts.　This　journal　is　©　the　Partner　Organisations