A　network-structured　SnO2/ZnO　heterojunction　nanocatalyst　with　high　photocatalytic　activity　was　successfully　synthesized　through　a　simple　two-step　solvothermal　method.　The　as-synthesized　samples　are　characterized　by　X-ray　diffraction,　X-ray　photoelectron　spectroscopy,　transmission　electron　microscopy,　scanning　electron　microscopy,　N2　physical　adsorption,　and　UV-vis　spectroscopy.　The　results　show　that　the　SnO2/ZnO　sample　with　a　molar　ratio　of　Sn/Zn　=　1　is　a　mesoporous　composite　material　composed　of　SnO2　and　ZnO.　The　photocatalytic　activity　of　SnO2/ZnO　heterojunction　nanocatalysts　for　the　degradation　of　methyl　orange　is　much　higher　than　those　of　solvothermally　synthesized　SnO2　and　ZnO　samples,　which　can　be　attributed　to　the　SnO2-ZnO　heterojunction,　the　pore　structure,　and　higher　Brunauer-Emmett-Teller　(BET)　surface　area　of　the　sample:　(1)　The　SnO2-ZnO　heterojunction　improves　the　separation　of　photogenerated　electron-hole　pairs　due　to　the　potential　energy　differences　between　SnO2　and　ZnO,　thus　enhancing　the　photocatalytic　activity.　(2)　The　SnO2/ZnO　sample　might　possess　more　surface　reaction　sites　and　adsorb　and　transport　more　dye　molecules　due　to　the　higher　BET　surface　area　and　many　pore　channels,　also　leading　to　higher　photocatalytic　activity.©　2009　American　Chemical　Society.