The author describes a new method for determining the phosphorus fixation by soils. It consists in growing plants on fertilized and unfertilized soils with soluble phosphate labelled with 15 p32. Rice plants were used as test plant. They were grown during 18 days. After the harvest the specific activity was determinated. The following equation was applied: F = capacity of soil phosphorus fixation; G = quantity of phosphorus added to soil; B = quantity of standard phosphorus applied; C O = specific activity of the phosphorus in the standard fertilizer; C = specific activity of the phosphorus contained in the plants grown on the soil unfertilized with phosphorus C1 = specific activity of the phosphorus in the plants grown on the soil fertilized with phosphorus.