The complexation of tungsten (VI) with an azo compound synthesized from para-tret-butylphenol (2-hydroxy-5-Tr-butylphenol-4-nitro-asobenzene) has been studied spectrophoto¬metrically. The optimum pH values of the solution are 2.0-3.0. The maximum light absorption of the complexes in n-butanol is in the range 460-470nm, and that of the reagent at 360-370; complex formation is accompanied by a bathochromic shift. The spectrophotometric characteristics of the complex have been calculated and the composition of the complex was determined by various methods. Using the equilibrium shift and isomolar series methods it has been found that the W:R ratio is 1:2. By the Sommer method it has been found that during complex formation one proton is released from each reagent molecule. The complex stability constant βk = 9.04·108 and the complex formation reaction equilibrium constant (4.2·104) have been calculated by the method of Komar. The molar absorption coefficient is (3.44.2).104. The graduation diagram is linear at a tungsten concentration of 1.0-10 µg/ml, n-butanol has been used as an extractant. A single extraction with n-butanol 97% of tungsten as a complex is extracted. Methods of extraction-atomic-absorption and extraction-photometric determination of tungsten have been developed and the influence of a number of extraneous ions on the determination of tungsten has been revealed. The correctness of the results obtained has been controlled by analysing the State Standard Alloy Reference Materials