A　series　of　Mo-doped　ZnO　photocatalysts　with　different　Mo-dopant　concentrations　have　been　prepared　by　a　grinding-　calcination　method.　The　structure　of　these　photocatalysts　was　characterized　by　a　variety　of　methods,　including　N2　physical　adsorption,　X-ray　diffraction　(XRD),　scanning　electron　microscopy　(SEM),　Fourier　transform　infrared　(FT-IR)　spectroscopy,　photoluminescence　(PL)　emission　spectroscopy,　and　UV-vis　diffuse　reflectance　spectroscopy　(DRS).　It　was　found　that　Mo6+　could　enter　into　the　crystal　lattice　of　ZnO　due　to　the　radius　of　Mo6+　(0.065　nm)　being　smaller　than　that　of　Zn2+　(0.083　nm).　XRD　results　indicated　that　Mo6+　suppressed　the　growth　of　ZnO　crystals.　The　FT-IR　spectroscopy　results　showed　that　the　ZnO　with　2　wt.%　Mo-doping　has　a　higher　level　of　surface　hydroxyl　groups　than　pure　ZnO.　PL　spectroscopy　indicated　that　ZnO　with　2　wt.%　Mo-doping　also　exhibited　the　largest　reduction　in　the　intensity　of　the　emission　peak　at　390　nm　caused　by　the　recombination　of　photogenerated　hole-electron　pairs.　The　activities　of　the　Mo-doped　ZnO　photocatalysts　were　investigated　in　the　photocatalytic　degradation　of　acid　orange　II　under　UV　light　(λ　=　365　nm)　irradiation.　It　was　found　that　ZnO　with　2　wt.%　Mo-doping　showed　much　higher　photocatalytic　activity　and　stability　than　pure　ZnO.　The　high　photocatalytic　performance　of　the　Mo-doped　ZnO　can　be　attributed　to　a　great　improvement　in　the　surface　properties　of　ZnO,　higher　crystallinity　and　lower　recombination　rate　of　photogenerated　hole-electron　(e-/h+)　pairs.　Moreover,　the　undoped　Mo　species　may　exist　in　the　form　of　MoO3　and　form　MoO　3/ZnO　heterojunctions　which　further　favors　the　separation　of　e　-/h+　pairs.　©　Science　China　Press　and　Springer-Verlag　Berlin　Heidelberg　2012.