This study aims to synthesize and characterize silica nanoparticles derived from rice husks of the local variety Dayang Rindu, and to evaluate their potential to reduce the toxicity of aluminum (Al) and iron (Fe) in Ultisol soils. Rice husks were collected from the Dayang Rindu farmer group in Muara Kelingi District, Musi Rawas Regency, South Sumatra. The synthesis process is carried out by calcination at temperatures of 200°C, 400°C, and 600°C, followed by the formation of a gel from a solution of Na₂SiO₃ using 1 M HCl until the pH reaches 7. The gel is dried at 80°C for 12 hours and calcined at 400°C for 3 hours using a Thermolyne FB 1410M-33 furnace to produce powdered silica nanoparticles. The characterization results showed that increasing the calcination temperature decreased particle size from 209 nm (200°C) to 122 nm (600°C), with a polydispersity index (PDI) of 0.021–0.038, indicating a uniform particle size distribution. The potential zeta value reaches 88.0 mV at 600°C, indicating excellent dispersion stability. SEM and TEM observations revealed spherical particles with smooth, homogeneous surfaces. The best characteristics are obtained at 600°C with a particle size of 122 nm, high stability, and a large specific surface area. The best results with silica nanoparticles were then used to test the reduction in Al and Fe toxicity in Ultisol soil at doses of 10–80 ppm. The results of the incubation test showed that a higher dose of silica nanoparticles significantly reduced Al³⁺ and Fe²⁺/Fe³⁺ levels in the soil via adsorption and the formation of silanol surface complexes (Si–OH). Overall, silica nanoparticles derived from Dayang Rindu rice husks have the potential to serve as an environmentally friendly ameliorant to reduce heavy metal toxicity in acidic soils and increase the productivity of tropical farmland.