A　novel　nanocrystalline　Pb2Sn2O6　photocatalyst　was　prepared　successfully　for　the　first　time　by　a　hydrothermal　process　at　180　degrees　C　for　12　h.　The　samples　were　characterized　by　an　x-ray　diffractometer　(XRD),　scanning　electron　microscope　(SEM),　transmission　electron　microscope　(TEM),　surface　area　(BET)　and　ultraviolet-visible　(UV-vis)　spectroscopes.　The　results　showed　that　the　pH　value　played　an　important　role　in　controlling　the　phase　formation　and　crystallite　sizes　of　the　Pb2Sn2O6.　A　single　phase　could　be　obtained　at　a　pH　＞=　9.　A　possible　reaction　mechanism　in　the　hydrothermal　process　was　also　proposed.　The　average　particle　size　for　the　sample　prepared　at　pH　=　13　was　only　about　9　nm,　and　the　BET　surface　area　was　as　large　as　76.7　m(2)　g(-1).　The　N-2　adsorption-desorption　isotherms　and　pore　size　distribution　curve　demonstrate　a　mesoporous　structure　with　a　narrow　pore　size　distribution.　As　a　novel　photocatalyst,　the　prepared　Pb2Sn2O6　samples　exhibit　powerful　photocatalytic　activity　for　the　decomposition　of　methyl　orange　under　365　nm　UV　light　irradiation.　Furthermore,　it　was　found　that　the　degradation　process　may　be　initiated　directly　by　photogenerated　holes　rather　than　commonly　sensed　hydroxyl　radicals.