Information on distribution of heavy metals in various chemical forms in soils may have greater chemical and biological significance than that of just total concentration. The amount of an isotopically exchangeable metal in soil solution, also called E-value, may conceptually best represent the fraction of the metal that is in dynamic equilibrium in the solution phase, and is considered to be a better indicator of availability of the chemically reactive metal to plants. Mercury (Hg) is of great concern in soil because it is phytotoxic to plants through accumulation in plant tissues and detrimental to human health through the food chain. In order to assess its phytotoxicity to vegetables and potential risk to human health, it is very important to have a better knowledge about labile pools of Hg in soils. The aim of this study is to determine the pools of isotopically exchangeable Hg ( E-value) in different soils. E-values of Hg in two typical soils (red soil and fluvo-aquic soil) was measured using the stable isotope ²⁰²Hg dilution technique and E_{1 min}, E_{1 min-24 h min}and E> _{> 24 h} values of Hg in the soils were calculated based on the model of isotopic exchange kinetics (IEK) with an iterative nonlinear regression algorithm. In addition, pools of labile Hg in the soils were also determined with four different single chemical extraction methods and a sequential extraction procedure (modified BCR approach) for comparison. Results show that 24 h after the addition of ²⁰²Hg, equilibrium of ²⁰²Hg/²⁰⁰Hg between soil and solution was established in both soils. The IEK equation was found fitting quite ideally the dynamics of isotope ratios and E_t values of Hg in soils. All the three compartments of E_{1 min}, E_{1 min-24 h min}and E_{> 24 h} in the red soil were markedly higher than those in the fluvo-aquic soil. E _a values, sum of E_{1 min} and E_{1 min-24 h min} and around 38%~60% of total Hg, obtained using the isotope method, were significantly higher than that (10%~15% of total Hg) acquired through extraction with 0.03% TGA-1/15 mol L^-1 Na₂HPO₄ being the highest among the 4 single extraction methods, and than ∑_BCR (20%~27%, sum of acid-extractable, reducible and oxidizable fractions) of the sequential extraction method. It was also found that soil pH had marked influence on E-values of Hg in the two studied soils. Compared with the chemical extraction procedures, the isotope method may yield E _a, which tends to be a bit too higher when used as indictor of content of soil available Hg. It is, probably, related to fixation of the spiked extraneous ²⁰²Hg by the soils and properties of the soil suspensions for E measurement.