Regolith-hosted rare earth element (REE) deposits have been the focus of recent studies. Most studies concern deposits formed over granites and felsic volcanic rocks, but little is known about those deposits developedover silica-undersaturated alkaline igneous rocks. The recently discovered Puxiong REE deposit in SouthwestChina formed through the weathering of nepheline syenite that has REE concentrations ranging from 177 to9,336 ppm. Hydrothermal processes partially enriched the parent nepheline syenite in REEs. About 60% of theREEs in the bedrock are hosted in britholite-(Ce), tritomite-(Ce), and cerite-(Ce) and ~21% in REE mineralsthat occur as inclusions in K-feldspar, with the rest in titanite, hiortdahlite, apatite, fluorite, and calcite. Theseminerals all can be easily decomposed to release REEs into soil solutions during weathering. The releasedREEs are adsorbed on clay minerals or precipitate as supergene rhabdophane and an Fe-Mn-REE oxyhydroxide phase. Nepheline syenite-derived regolith-hosted REE deposits are enriched in illite and halloysite, whichhave a higher ion exchange capacity than the parent granites. Illite formed through the weathering of primaryalkali minerals in the nepheline syenite.In the strongly eroded midslope and valley, the regolith has the lowest total REE concentration (997 and1,001 ppm on average, respectively) across the ore-bearing catchment, whereas the regolith in the hilltop andfootslope has REE concentrations of up to 1,564 and 1,677 ppm, respectively. Moreover, regolith at the footslope has the highest heavy REE (HREE) concentration of 110 ppm on average. The light REEs (LREEs)tend to be concentrated in the B horizon and laterally across the hilltops, whereas the HREEs are mobilizedby groundwater and soil solutions and accumulated in the upper C horizon vertically and the footslope profileslaterally. In conclusion, nepheline syenite was hydrothermally enriched in the REEs, and these elements werereleased to the weathering solution and then adsorbed onto clay minerals in sufficient concentrations to formeconomic regolith-hosted REE deposits. This process, which was controlled at Puxiong by the nature of clayminerals, pH, the redox conditions, the mobility of the REEs, and topography, led to maximum enrichment ofthe LREEs in the lower B horizon at the hilltop, and HREE enrichment in the upper C horizons vertically andin the footslope laterally.