By simulating oxalic acid/oxalate concentrations in forest litter leachate, a series of experiments were conducted including one-time extraction and repeated sequential extraction, with the oxalate loading rate varying from 0 to 200 mmol kg^-1 soil.Oxalic acid loading substantially stimulated soil-P-release from A₁ horizon, showing a linear relationship;but its effect on B horizon soil was relat ively negligible, especially at low oxalic acid concentrations (< 5 mmol L^-1).Oxalate solutions (0.5~20.0 mmol L^-1) oxalic acid adjusted to pH 5.16 with 10.0 mmol L^-1 NaOH) had a much higher (1.51~2.98 times) soil P re lease effect than oxalic acid solut ion the same in oxalate concentration.Therefore, the mechanism of oxalic acid/oxalate triggering release of soil phosphorus is assumed to be dominated by ligand-exchange or complexing reactions of oxalate anion(C₂O₄^2-), but not simply acid-dissolving effect.The effect of oxalate anion on soil phosphorus release was found to be somewhat cumula tive, i.e.the amount of P released was primarily controlled by the cumulative oxalate loading rate, relatively independent of the manner of oxalate addition (one-time or sequential).When oxalate anion was loaded as pH 5.16 sodium oxalate solution, the regression equation between A₁ horizon soil P release (mg kg^-1) and cumulative oxalic loading rate (mmol kg^-1) was: Y=-0.0004X²+0.1766X+0.4253,R²=0.9902.Merely on a quantitative basis of oxalate anion leached from forest litter, the increased soil P release from A₁ horizon (0~20 cm) was estimated to be 2.40 kg hm^-2 a^-1, accounting for 1/3~1/5 of the annual P absorption in middle-aged forests.If other types of organic anion or other react ions producing organic anion were taken into account, the cumulative effect of organic anions on soil P release would be very conspicuous.