Defect　engineering　in　metal　organic　frameworks　(MOFs)　has　captured　significant　attention　in　the　field　of　photocatalysis.　A　series　of　UiO-66(Ce)　(UiO　=　University　of　Oslo)　MOFs　with　different　contents　of　missing-linker　defects　have　been　developed　for　the　photocatalytic　selective　oxidation　of　benzylamine　(BA)　and　thioanisole　(TA)　under　visible　light.　The　introduction　of　missing-linker　defects　promotes　the　formation　of　unsaturated　Ce　sites　with　a　high　Ce3+　content.　It　also　generates　a　high　concentration　of　oxygen　vacancies.　In　situ　Fourier　transform　infrared　spectroscopy　(FTIR)　results　revealed　that　BA　and　TA　molecules　were　activated　on　coordinatively　unsaturated　Ce　sites　via　the　H-NCe　and　the　C-SCe　interactions,　respectively.　Simulated　in　situ　electron　paramagnetic　resonance　(EPR)　data　indicate　that　O-2　activation　and　reduction　occur　at　coordinatively　unsaturated　Ce3+　sites　to　form　O-2(-).　This　is　accelerated　by　the　Ce3+/Ce4+　redox　cycle　associated　with　the　photogenerated　electrons.　The　corresponding　photogenerated　holes　are　involved　in　the　deprotonation　of　the　activated　BA　and　TA.　The　most　active　sample　exhibits　98.4%　and　95.5%　conversion　rates　for　BA　and　TA　oxidation.　Mechanisms　for　the　molecular　activation　are　proposed　at　the　molecular　level.