Two-dimensional　(2D)　organic-inorganic　hybrid　perovskite　materials　have　received　substantial　attention　because　of　their　exceptional　optoelectronic　properties.　Although　the　applications　of　2D　perovskite　nanosheets　are　promising　in　various　optoelectronic　devices,　which　all　face　harsh　working　conditions　of　light　exposure,　little　is　known　about　the　photo-stability　and　degradation　mechanisms　of　these　2D　perovskite　nanosheets.　In　this　work,　degradation　of　(C4H9NH3)(2)PbBr4　(BA(2)PbBr(4))　nanosheets　when　exposed　to　ultraviolet　(UV)　light　and　white　light　is　explored.　The　morphology,　optical　properties,　and　microstructure　of　the　nanosheets,　under　different　conditions　of　light　exposure,　was　studied　in　detail.　UV　light　is　more　destructive　compared　to　white　light,　which　both　led　to　a　nanosheet　breakdown.　A　combination　of　transmission　electron　microscopy　(TEM)　imaging　and　electron　diffraction　revealed　that　the　organic　moieties　are　most　sensitive　to　light　exposure　and　partial　disorder　toward　complete　disorder　takes　place　during　light　exposure.　Moreover,　excessive　light　exposure　further　causes　a　[PbBr6](4-)　octahedron　tilt　and　re-ordering　within　the　perovskite　structure.　This　study　could　enrich　the　understanding　of　2D　perovskite　nanosheets　and　their　photostability,　offer　a　new　perspective　in　interpreting　the　light-perovskite　interaction,　and　further　help　the　design　of　robust　and　light-tunable　2D　perovskite-based　optoelectronic　devices.