The concentrations of thiotungstates formed under various experimental conditions simulating natural aquatic environments were quantitatively determined by an ultraviolet/visible spectrophotometer, with their effects on the formation and species transformation of thiotungstates being evaluated. The results demonstrate that weakly acidic to neutral pH values were necessary for the substantial formation of mono-, di-, tri-, and tetra-thiotungstates, especially tri-and tetra-thiotungstates, and the thiolation of tungstate to the highest degree occurred at pH=5. Under acidic conditions, thiotungstates were prone to be the major species of tungsten even at relatively low molar ratios of sulfide to tungsten (e.g. S(Ⅱ)/W ratio=10:1).With an increase of S(Ⅱ)/W ratio to 20:1, complete thiolation of tungstate was observed, and the dominant species of tungsten became mono-thiotungstate WO₃S^2-. At S(Ⅱ)/W ratios of 30:1and 40:1, di-and tri-thiotungstates WOS₃^2- predominated in the solutions, respectively. Moreover, for the acidic solutions, the increase of ionic strength obviously inhibited the thiotungstate-forming reactions. In contrast, the variation of solution ionic strength had little effect on the tungsten speciation under neutral conditions.