Three-dimensional (3D) dandelion-like TiO2 nanostructures were successfully synthesized from TiCl4 and water via simple hydrothermal method. The samples were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET). The photocatalytic activity of the dandelion-like TiO2 nanostructures was evaluated by photoreduction of Cr(VI) under UV light irradiation. The results indicated that the dandelion-like rutile TiO2 nanostructures were composed of ordered nanorods with an average diameter of 17 nm. Furthermore the results indicated that the dandelion-like TiO2 can be easily scaled-up and reproducible. The growth mechanism of the dandelion-like TiO2 nanostructures has been proposed to occur in a four-step reaction, i.e., (i) nucleation and nanoparticle formation; (ii) formation of spheres through self-assembly growth; (iii) further growth and (iv) agglomeration of the dandelions to form flower-like rutile TiO2. The dandelion-like TiO2 structures exhibited higher photocatalytic efficiency compared to P25 TiO2 for the photoreduction of Cr(VI). The highest photocatalytic reduction rate was with 2 g of the catalyst in a 10 mg/L Cr(VI) solution with pH 2. The high photocatalytic activity of the dandelion-like TiO2 nanostructures was attributed to the flower-like morphology, highest light-harvesting efficiency resulted from multiple reflections of light, hierarchical mesoporous structure and large specific surface area (81 m2/g).