Abstract: Clay fractions from four soils were analyzed for kaolinite and gibbsite by differential thermal analysis (DTA) and selective dissolution analysis (SDA). The kaolinite values by the two methods had a standard deviation of ±0.95 for the 2−0.2 µ clay of the three most highly weathered soils. Apparently some kaolinite was dissolved with amorphous material in the 0.2–0.08 µ kaolinite standard and probably in 0.2–0.08 µ soil clays. Accuracy of kaolinite determination for the 0.2–0.08 µ soil clays by DTA was reduced because of uncertainty of exact composition of the standard. Presence of montmorillonite in Sango soil clays, particularly the 0.2–0.08 µ fraction, apparently contributed to the error in kaolinite determination by SDA. More precise values for gibbsite were obtained by DTA than by SDA because of the dissolution of alumina from sources other than gibbsite.