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The AL-P25 composites(AL = alizarin,P25 = nano titanium dioxide)with oxygen vacancies were synthe-sized by a simple hydrothermal method and applied for the photoreduction of Cr(Ⅵ)under visible light.The AL-P25 composites were characterized by scanning electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy analysis,Fourier transform infrared spectrometer,thermo-gravimetric analysis,UV-vis diffuse reflectance spectroscopy,photoluminescence spectroscopy and electron paramagnetic resonance spectroscopy.The results sug-gested that the AL-P25 composites were successfully prepared,and alizarin was linked to P25 via Ti-O-C bonds.AL-P25 composites represented excel-lent photoreduction efficiency on Cr(Ⅵ)under visible light,which was 99.4％after 60 min of illumination.Finally,a photocatalytic mechanism of AL-P25 composites was proposed that ligand-metal charge transfer(LMCT)process between alizarin and P25 effectively enhances separation efficiency of photo-generated electrons and holes.