For the extraction of reducing compounds from paddy soils, a 0.1M Al₂(SO₄)₃ solution of pH 2.5 was proposed. It was found that the extracting power of this solution was strongest among the eight tested solutions, and owing to the strong buffeting capacity of the Al₂(SO₄)₃ solution, the pH values of the equilibrium solutions for different types of soils fluctuated within only a narrow range (2.65-3.15). A soilaolutian ratio of 1:20 and stirring for 5 minutes were sufficient. The extracting solution possesses the further advantage that various reducing compounds may be determined directly in separate aliquots without preliminary separation, which is necessary for determining the easily oxidizable compounds when in contact with the air. The reducing compounds were determined as manganous Mn, ferrous iron, active organic reducing compounds oxidizable by titration with permanganate at room temperature and non-active organic reducing compounds oxidizable by heating with dichromate at 90-95℃ for 20 minutes. Since the amount of extracted active organic reducing compounds is ra.her constant between pH 2.5 and 6.5 and the extracted iron is dependent on the pH value of the equilibrium solution, it is considered that the active organic reducing compounds represented a definite group of easily extracted compounds and is quite reversible with respect to oxidation-reduction reactions, whereas a large part of the ferrous compounds may exist in forms of hydroxide, sulfide and bicarbonate.