Nanocrystalline　PbBi2Nb2O9　was　successfully　prepared　by　a　modified　sol-gel　method.　The　as-prepared　nanocrystalline　PbBi2Nb2O9　was　an　active　visible-light-driven　photocatalyst　for　the　photoreduction　of　4-nitroaniline　to　p-phenylenediamine　in　aqueous　solution　upon　purging　with　N-2.　Its　photocatalytic　activity　was　determined　by　the　balance　between　the　surface　area　and　crystallinity.　The　best　sample　was　obtained　after　calcination　at　650　degrees　C,　giving　4-nitroaniline　conversion　of　similar　to　100%　and　p-phenylenediamine　selectivity　of　similar　to　99%　after　irradiation　for　150　min,　which　was　much　higher　than　those　of　bulk　PbBi2Nb2O9　and　TiO2-xNx　photocatalysts.　Further　experiments　revealed　that　oxalate　anion　(as　a　hole　scavenger)　was　indispensable　for　the　photocatalytic　reduction　of　4-nitroaniline.　Moreover,　on　the　basis　of　the　electron　spin　resonance　analysis　result,　a　mechanism　was　proposed　to　explain　the　photoreduction　of　4-nitroaniline　over　nanocrystalline　PbBi2Nb2O9.　(c)　2012　Elsevier　Inc.　All　rights　reserved.