The photocatalytic reduction of Cr(VI) on TiO 2 nanoparticle modified with phthalic acid, which was prepared through a chemisorption method, has been investigated under ultraviolet light irradiation. This study found that the adsorption of phthalic acid onto the surface of TiO 2 nanoparticle resulted in the formation of a surface-modified complex. The interaction of TiO 2 with phthalic acid was characterized by various spectroscopic methods including diffuse reflectance UV–vis, infrared, fluorescence spectra, and X-ray diffraction (XRD). The results indicated that the recombination of charge carriers was effectively suppressed due to the modification of phthalic acid on the surface of TiO 2 . In addition, the modified TiO 2 resulted in enhanced photocatalytic reduction activity for Cr(VI), which might be attributed to the effective separation of electron–hole pairs.