Dissolution by acid oxalate solution was investigated as a means of determination and removal of allophane and iron and aluminium oxides in clays. Allophane and amorphous oxides of iron and aluminium were selectively dissolved in 0.15 M acid oxalate solution of pH 3.5 by shaking for 1 hour at 30°C or 3 hours at 20°C, provided the ratio of sample weight to solution volume was 100 mg to 200 ml. Dissolved silica was determined directly by a heteropoly blue method and aluminium and iron were determined as ferron complexes after removal of the oxalate by H₂SO₄-HNO₃ treatment. Crystalline clay minerals such as kaolinite, halloysite, metahalloysite, montmorillonite, gibbsite, hematite and goethite were hardly dissolved by the same procedure.