In this paper, the Mo(V)-thiocyanate complexing reaction in the acidic aqueous solution without surfactant or organic solvent was studied. It was found that the Mo(V)-thiocyanate complexes could be stable for 4 h at least in the 50 mL solution containing 7.5 mL H2SO4 (1:1), 4 mL HClO4 (1:1), 3 mg Fe2+ and 4 mL vitamin C (6%). The absorption spectrum of Mo(V)-thiocyanate complexes under this condition was studied, a peak of 460 nm was found and the maximal molar absorption coefficient was determined to be 1.02 x 10(4). The reaction mechanism of the Mo(V)-thiocyanate complexes was determined to be a three-grade complexing reaction by using the equilibrium movement method. Meanwhile, the stable constants of all kinds of grades complexes was determined by the [symbol: see text] method to be beta 1 = 15.63, beta 2 = 174.4 and beta 3 = 1,502, and the corresponding molar absorption coefficients were delta epsilon 1 = 8,957, delta epsilon 2 = 9,347 and delta epsilon 3 = 10,610, respectively.