Nanocrystalline　BiVO4　powders　were　prepared　from　aqueous　Bi　(NO3)(3)　and　NaVO3　solution　by　a　rapid　microwave-assisted　method　with　accurate　controlled　of　microwave　irradiation　time.　The　properties　of　the　synthesized　BiVO4　powders　were　investigated　by　XRD,　FFIR,　TEM　and　UV-Vis.　When　beating　10　min　by　microwave,　pure　tetragonal　BiVO4　can　be　obtained.　The　highly　crystalline　phases　converted　irreversibly　from　tetragonal　to　monoclinic　BiVO4　with　prolonged　irradiation　time.　When　heating　above　40　min　by　microwave,　pure　monoclinic　BiVO4　can　be　obtained.　X-ray　diffraction　and　FTIR　measurements　proved　the　phase　transition　of　BiVO4.　These　variations　in　phase　structures　result　in　different　photocatalytic　properties　under　visible　light.