CaSb2O5(OH)2　nanocrystals　were　synthesized　via　a　facile　microwave-hydrothermal　method.　The　physico-chemical　properties　of　the　as-synthesized　CaSb2O5(OH)2　photocatalyst　were　characterized　by　X-ray　diffraction,　UV-vis　diffuse　reflectance　spectroscopy,　transmission　electron　microscopy,　electron　spin　resonance,　and　X-ray　photoelectron　spectroscopy.　The　photocatalytic　activity　was　evaluated　by　the　decomposition　of　rhodamine　B,　methyl　orange,　and　methylene　blue　in　aqueous　solution　under　UV　irradiation.　For　comparison　purposes,　we　have　also　investigated　the　activity　of　TiO2　(P25,　Degussa　Co.)　under　the　same　condition.　The　results　revealed　that　the　sample　had　a　much　higher　photocatalytic　activity　than　that　of　P25.　The　high　activity　and　long-term　stability　of　CaSb2O5(OH)2　were　mainly　attributed　to　its　stronger　oxidative　capability　and　larger　specific　surface　area　in　comparison　with　P25.　This　article　presents　a　detailed　analysis　of　the　intermediates　produced　in　the　photocatalytic　reactions　using　the　liquid　chromatography　-　mass　spectrometry　technique.　The　possible　photocatalytic　reaction　pathways　as　to　how　CaSb2O5(OH)2　nanocrystals　degrade　organic　dyes　have　also　been　proposed.　©　2009　American　Chemical　Society.