In　this　work,　an　upconversion　luminescence　(UCL)　nanosensor　for　fast　detection　of　ferric　ion　(Fe3+)　and　phosphate　ion　(Pi)　is　developed　based　on　the　inner-filter　effect　(IFE)　between　NaYF4:Yb/Er　upconversion　nanoparticles　(UCNPs)　and　Fe3+-hypocrellin　B　(HB)　complex.　Fe3+-HB　complex　has　strong　absorption　band　(450–650 nm),　which　overlaps　with　the　green　emission　peak　of　UCNPs　at　545 nm.　By　adding　Fe3+　and　Pi,　the　UCNPs-HB　system　produces　the　red-shift　change　of　absorption　spectrum,　which　leads　to　the　＇on–off-on＇　process　of　IFE.　So,　with　the　specific　recognition　ability　of　HB　for　Fe3+　and　the　competitive　complexation　of　Pi　for　Fe3+,　the　proposed　nanosensor　utilizes　the　UCL　change　to　achieve　the　detection　of　the　targets.　For　the　detections　of　Fe3+,　the　linear　range　is　10–600 μM　with　a　limit　of　detection　(LOD)　of　2.62 μM,　and　for　Pi,　the　linear　range　is　5–100 μM　with　a　LOD　of　1.25 μM.　The　results　for　selectivity,　precision,　and　recovery　test　are　also　satisfactory.　Furthermore,　the　real　sample　detection　shows　that　the　proposed　nanaosensor　has　a　great　potential　in　environmental　and　biological　systems.　Graphical　Abstract:　An　upconversion　luminescence　(UCL)　nanosensor　based　on　the　inner-filter　effect　(IFE)　between　upconversion　nanoparticles　(UCNPs)　and　Fe3+-hypocrellin　B　(HB)　complex　for　the　detection　of　Fe3+　and　phosphate　ion　has　been　proposed,　which　is　promising　to　be　a　convenient　and　sensitive　assay　for　monitoring　Fe3+　and　phosphate　ion　in　different　environments　and　biological　systems.　[Figure　not　available:　see　fulltext.]　©　2023,　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH,　DE　part　of　Springer　Nature.