Thallium (Tl) is a highly toxic trace element and listed as one of the USEPA priority pollutants. Although Tl(I) is highly toxic, its fate in soil has not been well understood. In soil environments, adsorption and desorption reactions predominately determine the mobility and availability of contaminants in soils. To understand the underlying mechanisms of Tl adsorption/desorption of soils, this study performed Tl(I) adsorption and desorption experiments on two groups of soil samples (i.e., permanent-charge and pH-dependent-charge soils), which have different mineralogical and physicochemical properties. The experimental results show that Tl(I) adsorption capacities of permanent-charge soils were higher than those of the pH-dependent-charge soils. The ratios of Tl(I) adsorption maximum to the corresponding cation exchange capacity (CEC) were determined to be 16 to 32% for pH-dependent-charge soils and up to 76% for permanent-charge soils. The results of Tl L3-edge X-ray absorption near-edge structure (XANES) spectra suggest that the overall Tl(I) adsorption was mainly attributed to clay minerals including vermiculite, illite and smectite. Subsequently, the adsorption/desorption isotherms of each soil were fitted to Freundlich equation to evaluate the tendency of desorption as well as to calculate the hysteresis index. The permanent-charge soils exhibited greater degrees of the hysteresis effect in comparison to the pH-dependent-charge soils, indicating greater Tl mobility and availability of the pH-dependent-charge soils. To authors’ best knowledge, this is the first time that adsorption and desorption of Tl(I) were both investigated on soils. The results revealed the relatively high mobility of Tl(I) in soils, implying a high environmental risk of Tl(I) in soils.