Sulfate heave in chemically treated soils has been recognized as a major concern in pavement construction projects. Sulfate measurements on pavement subgrade soils are an important step in designing an appropriate soil stabilization scheme. Various methods have been developed for measuring soluble sulfates based on gravimetric and turbidity procedures. Variations have been observed in measuring soluble sulfate levels among these methods, hence a need arises to compare and validate each of these methods. In the present paper a comparative study of three methods namely AASHTO method, modified UTA method and TxDOT method is made for determining soluble sulfates of natural clayey soils. Two natural clayey soils are mixed with known amounts of sulfates in the form of sodium sulfate at four different concentrations of 1500, 3000, 5000 and 10000 ppm. Measurement of soluble sulfates is carried out using the above three methods. Test results are fully analyzed and evaluated for repeatability of each method in measuring true amounts of sulfates in soils. Methods are also evaluated in providing realistic measurements with respect to sulfate levels.