As an emerging contaminant, tungsten (W) displays unexpectedly high mobility in soil despite its extremely low solubility, challenging current scientific understanding. This paradox underscores the limited knowledge regarding the specific W species responsible for its high mobility. In this study, a series of field and incubation experiments were conducted across multiple soil types to investigate the distribution and speciation of W in soil porewater, widely known as ″the most mobile fraction″. Ultrafiltration analysis revealed that W in soil porewater predominantly existed in colloidal-size (5 kDa–0.45 μm) phases rather than the ″truly-dissolved″ phase (<5 kDa). Especially in deeper soil layers approaching shallow groundwater, colloidal W content exceeded 93 %. XANES spectra showed that colloidal W was mainly in the hexavalent state (W^VI), and insoluble W metal (W⁰) entering the soil could rapidly oxidize into W^VI through biotic or abiotic processes. Advanced characterizations, including STEM-EDS-SAED, SEM-EDS, and SR-XRF, identified aluminosilicate mineral colloids as the primary carrier for W in soil porewater. Within these W-bearing aluminosilicate mineral colloids, W was primarily present as Al₂(WO₄)₃ precipitates with a W–Al distance of ∼ 3.64 Å, as confirmed by EXAFS. Additionally, a minor fraction of silicotungstates was also detected in the colloidal fraction using XAS and STEM-EDS-SAED. These two species were further substantiated through geochemical modeling and density functional theory (DFT) analysis. Importantly, this study hypothesizes that the associations of W with aluminosilicate mineral colloids and silicotungstates are widespread across different soil types. The finding suggests that colloid-associated W mobility is a dominant yet previously overlooked process, helping to explain why W, despite its low solubility, exhibits exceptionally high mobility in soils.