Heavy metal contamination of soils has increased in the past few decades due to industrial activities, use of industry byproducts in agriculture, land disposal of wastes, and application of fertilizers and chemicals. Variable charge soils are generally more vulnerable to heavy metal contamination because of their low organic matter content and a small cation exchange capacity as well as being acidic. The movement and bioavailability of heavy metals in most agricultural soils of tropical and subtropical regions is mainly controlled by adsorption-desorption processes. However, the adsorption-desorption behavior of heavy metals at contaminated levels is not fully understood. Heavy metals can be adsorbed onto surfaces of soil colloids through non-specific adsorption (by static electric force) and specific adsorption (formation of chemical bonds between the ion and the surface). Adsorption of copper (Cu²⁺), lead (Pb²⁺), and cadmium (Cd²⁺) in highly weathered variable charge soils involves both mechanisms. A series of studies were conducted to understand the adsorption-desorption behavior of Cu²⁺, Pb²⁺, and Cd²⁺ at contaminated levels in two representative variable charge soils in China, i.e. a REQ soil (clayey, kaolinitic thermic plinthite Aquult) and a RAR soil (clayey, mixed siliceous thermic typic Dystrochrept).The results indicate that adsorption of Cu²⁺, Pb²⁺, or Cd²⁺ resulted in a significant decrease in soil pH due to replacement of H⁺ and/or Al³⁺ from soil surfaces. The pH drop varied among the different metals in the order of Pb²⁺ (1.06-1.13 units) > Cd²⁺ (0.95-1.13 units)>Cu²⁺ (0.60-0.80 units) at the loading of 31.5 m mol kg^-1 soil. The REQ soil had a slightly greater pH decrease than the RAR soil at the same metal loadings. The moles of H⁺ released per mole of metal adsorbed in the RAR and REQ soil were 0.61–1.44 for Pb²⁺, 0.36-0.55 for Cd²⁺, and 1.12-2.57 for Cu²⁺. Adsorption of Pb²⁺, Cd²⁺, or Cu²⁺ in the variable charge soils consists of a fast reaction that lasted from 15 min to 2 h, followed by a slower but longer stage (up to 24 h). The isotherms of Cu²⁺, Pb²⁺, or Cd²⁺ adsorption fit well with some physical-chemical models, such as the Freundlich and the simple Langmuir equation. A maximum adsorption of each individual metal could be obtained from the Langmuir equation for comparing heavy metal holding capacity in different soils. The adsorption of Pb²⁺, Cd²⁺, or Cu²⁺ is generally pH-dependent, increasing with increasing pH. Temperature influenced Pb²⁺, Cd²⁺, or Cu²⁺ adsorption, but in a complicated manner. Presence of competitive cations reduced adsorption of any individual metals. The effects of inorganic anions on adsorption of Cu²⁺, Pb²⁺, or Cd²⁺ were dependent on anion types and apparently related to the altered surface properties caused by anion adsorption and/or the formation of anion-metal complexes. Addition of organic acids such as citric acid or oxalic acid at low concentrations slightly increased adsorption of Cu²⁺, Pb²⁺, and Cd²⁺ in variable charge soils but significantly decreased their adsorption at relatively high concentrations (>0.001 mol L^-1), likely because of chelating effects. Desorption of the adsorbed metals in the 0.01 mol L^-1 NaNO₃ was small for Pb²⁺, but moderate for Cd²⁺. The recovery of adsorbed Pb²⁺ by five successive desorption with 0.01 mol L^-1 NaNO₃ solution was 0-19%, depending on adsorption saturation, and the corresponding value for Cd²⁺ was 0-53%, indicating that Pb²⁺ is more tightly bound in the variable charge soils than Cd²⁺. Approximately 61 to 95% of the adsorbed Cu²⁺ was desorbed by five successive extraction using 1 mol L^-1 NH₄Ac (pH 5.0), indicating that most of the adsorbed Cu²⁺ is bioavailable within a short time of adsorption.