The synthesis of N’-(3-trimethoxysilylpropyl) diethylentriamine modified silica (SiO2(RHA)-TMPDT) has been done. The silica source precursor was sodium silicate (Na2SiO3) obtained rice hull ash (RHA) and N’-(3-trimethoxysilylpropyl) diethylentriamine (TMPDT) was used as modifier. Furthermore, SiO2(RHA)-TMPDT were characterized using Fourier transform infrared (FTIR) spectrophotometer, scanning electron microscope (SEM-EDX), thermogravimetric analyzer (TGA) and surface area analyzer (SAA). Adsorption was carried out using batch system with pH variation, contact time and initial concentration of gold (III). FTIR spectra of SiO2(RHA)-TMPDT showed peaks at 1057, 1471 and 2908 cm-1 confirming Si-O-Si, NH2 and C-H stretching, respectively. SEM-EDX analysis showed the presence of C and N elements of 46.5 and 2.1%, respectively. TG analysis was characterized by a mass loss of 10.57% at (480-900) °C indicating the release of organic groups from TMPDT. Material of SiO2 (RHA)-TMPDT has surface area and pore diameter of 54.679 m²/g and 38.386 Å, respectively. The optimum adsorption of gold (III) on SiO2(RHA)-TMPDT was obtained at pH of 3.0. The kinetic study shows that the adsorption of Au (III) ion follows pseudo-2nd order. The study of adsorption isotherm of gold (III) on SiO2(RHA)-TMPDT follows Freundlich with an adsorption capacity of 1301 mg/g. The selectivity of Au3+/Zn2+, Au3+/Cu2+, Au3+/Fe3+ were 1.021, 0.164 and 0.113, respectively. [ABSTRACT FROM AUTHOR]