Rutin has been used for the spectrophotometric determination of vanadium (V). Vanadium (V) forms with rutin an orange water-soluble complex, which obeys Lambert-Beer’s law at 435 mµ within the concentration range of 0·51–14·3 p.p.m. of vanadium. The colour intensity of the complex does not vary between pH 3·5 and 6·0 and the molar composition of the complex shows that it contains vanadium and the rutin in the molar ratio of 1 : 2. The stability constant of the vanadium-rutin complex has been determined by the method based on Beer’s law. Limits of interference due to various cations and anions in this determination have been given.