Barium tin hydroxide/tin dioxide nanorods are synthesized by a facile hydrothermal method. The morphology, structure and optical performance of the nanorods are characterized via X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy and solid ultraviolet-visible (UV-vis) diffuse reflectance spectrum. The nanorods are mainly composed of monoclinic BaSn(OH) 6 and orthorhombic SnO 2 phases with the length and diameter of about 5 µm and 50-150 nm, respectively. The formation process of the nanorods is investigated based on the morphology and structure evolution of the products from different hydrothermal conditions. Solid UV-vis diffuse reflectance spectrum shows that the nanorods belong to typical semiconductor with the band gap of 3.74 eV. The barium tin hydroxide/tin dioxide nanorods are used for the photocatalytic degradation of gentian violet under UV light irradiation. The degradation efficiency reaches 93.2% with the irradiation time of 8 h adding 10 mg nanorods in 10 mL 10 mg mL −1 gentian violet solution. The reactive species trapping results show that hydroxyl radicals, holes and superoxide radicals are main reactive species for gentian violet degradation. The barium tin hydroxide/tin dioxide nanorods are stable for the photocatalytic reaction of the gentian violet.