X-ray　imaging　plays　an　increasingly　crucial　role　in　clinical　radiography,　industrial　inspection,　and　military　applications.　However,　current　X-ray　imaging　technologies　have　difficulty　in　protecting　against　information　leakage　caused　by　brute　force　attacks　via　trial-and-error.　Here　high-confidentiality　X-ray　imaging　encryption　by　fabricating　ultralong　radioluminescence　memory　films　composed　of　lanthanide-activated　nanoscintillators　(NaLuF4:　Gd3+　or　Ce3+)　with　imperceptible　purely-ultraviolet　(UV)　emission　is　reported.　Mechanistic　investigations　unveil　that　ultralong　X-ray　memory　is　attributed　to　the　long-lived　trapping　of　thermalized　charge　carriers　within　Frenkel　defect　states　and　subsequent　slow　release　in　the　form　of　imperceptible　radioluminescence.　The　encrypted　X-ray　imaging　can　be　securely　stored　in　the　memory　film　for　more　than　7　days　and　optically　decoded　by　perovskite　nanocrystal.　Importantly,　this　encryption　strategy　can　protect　X-ray　imaging　information　against　brute　force　trial-and-error　attacks　through　the　perception　of　lifetime　change　in　the　persistent　radioluminescence.　It　is　further　demonstrated　that　the　as-fabricated　flexible　memory　film　enables　achieving　of　3D　X-ray　imaging　encryption　of　curved　objects　with　a　high　spatial　resolution　of　20　lp/mm　and　excellent　recyclability.　This　study　provides　valuable　insights　into　the　fundamental　understanding　of　X-ray-to-UV　conversion　in　nanocrystal　lattices　and　opens　up　a　new　avenue　toward　the　development　of　high-confidential　3D　X-ray　imaging　encryption　technologies.　©　2023　Wiley-VCH　GmbH.