Microcrystalline　ABi(2)Nb(2)O(9)　(A=Sr,　Ba)　photocatalysts　were　successfully　synthesized　by　a　citrate　complex　method.　The　as-prepared　samples　were　characterized　by　the　X-ray　diffraction　technique,　BET　surface　area　analysis,　UV-vis　diffuse　reflectance　spectrum,　transmission　electron　microscopy,　X-ray　photoelectron　spectroscopy　and　inductively　coupled　plasma-atomic　emission　spectrometry.　The　results　indicated　that　single-phase　orthorhombic　SrBi2Nb2O9　could　be　obtained　after　being　calcined　above　650　degrees　C,　while　BaBi2Nb2O9　was　tetragonal.　Based　on　the　diffuse　reflectance　spectra,　the　band　gaps　of　the　obtained　samples　were　calculated　to　be　around　3.34-3.54　eV.　For　the　photocatalytic　redox　reaction　of　methyl　orange　under　UV-light　irradiation,　SrBi2Nb2O9　exhibited　higher　photocatalytic　activity　than　that　of　BaBi2Nb2O9.　The　effects　of　the　crystallinities,　BET　surface　areas　and　crystal　structures　of　the　samples　on　the　photocatalytic　activities　were　discussed　in　detail.　(C)　2010　Elsevier　Inc.　All　rights　reserved.