Urchin-like　LaPO4　hollow　spheres　were　successfully　synthesized　by　a　facile　solution　route　using　citric　acid　(CA)　as　a　structure-directing　agent.　The　size　of　the　three-dimensional　(3D)　hollow　spheres　was　tuned　by　changing　the　concentration　of　CA.　The　formation　mechanism　of　the　3D　LaPO4　hollow　spheres　was　revealed　by　studying　the　time-dependent　morphology　evolution　process.　Importantly,　compared　with　monodispersed　one-dimensional　(1D)　LaPO4　nanorods,　the　3D　LaPO4　hollow　spheres　self-assembled　from　nanorods　showed　a　6.8-fold　enhancement　in　photocatalytic　activity　for　CO2　reduction,　which　is　attributed　to　the　synergistic　effect　of　their　hierarchical　hollow　structure,　higher　light-harvesting　capacity,　and　faster　electron　transfer.　Our　findings　provide　not　only　a　simple,　facile　method　for　the　synthesis　of　hierarchical　hollow　micro/nanoarchitectures　but　also　an　efficient　route　for　enhancing　the　photocatalytic　performance.　[Figure　not　available:　see　fulltext.]　©　2017,　Tsinghua　University　Press　and　Springer-Verlag　Berlin　Heidelberg.