Ultrathin　BiOCl　nanosheets　(NST)　with　the　thickness　about　1.5　nm　was　prepared　as　a　photocatalyst　for　the　oxidation　of　benzylamine　(BA)　to　N-benzyleneamine　under　visible　light.　The　photocatalytic　activity　of　NST　is　over　2.5　times　higher　than　that　of　its　bulk　counterpart.　More　oxygen　vacancies　(OVs)　in　NST　were　revealed　by　EPR　and　XPS.　UV-DRS　result　indicates　that　light　adsorption　of　NST　can　be　extended　to　visible　light　due　to　the　presence　of　OVs.　In　addition,　rich　OVs　result　in　Bi　atoms　in　sublayer　to　be　exposed　as　Lewis　acid　sites.　In　situ　FTIR　spectrum　shows　that　BA　is　chemosorbed　on　the　Lewis　acid　sites　forming　surface　-N　center　dot　center　dot　center　dot　Bi-　coordination　species,　resulting　in　the　activation　of　BA.　The　surface　coordination　species　would　also　result　in　the　red　shift　of　the　photo-absorption　spectrum.　Finally,　a　synergistic　mechanism　based　on　surface　coordination　activation　and　photocatalysis　was　proposed　to　explain　the　enhanced　photocatalytic　activity　over　NST.　(C)　2019　Elsevier　Inc.　All　rights　reserved.