To evaluate conventional calcium dihydrogen phospahte [Ca(H2PO4)2] solution containing 500 mg P/L as an extractant for soluble plus adsorbed sulfate (SO4), we added known amounts of SO4to 10 soil samples differed in clay mineral composition and extracted with Ca(H2PO4)2solution. The experimental results showed that the five successive extractions at a soihsolution ratio of 1:10 could quantitatively recover the added SO4, and there was little effect of air‐drying the soils after addition of SO4. Based upon these experimental results, we concluded that the Ca(H2PO4)2extraction is an excellent method for determining soluble plus adsorbed inorganic SO4in soils.