This research aimed to synthesize silica microparticles from rice husk ash and modify its surface with humic acids. Silica was obtained by dissolution and thermal precipitation of rice husk ash using the sol-gel method via two approaches. Method I: the rice husk ash was refluxed with 2.5 M NaOH and Method II: the rice husk ash was refluxed with 1.5 M HCl before being refluxed with 2.5 M NaOH. The efficiency and purity of silica were compared. Fourier transform infrared spectral data showed the presence of hydrogen bonded silinol and siloxane groups in silica. X-ray diffraction pattern showed that the obtained products were amorphous silica. Silica that obtained by the method II has higher efficiency and purity than silica that obtained by the method I. The purity of the synthesized silica was 93.8 and 79.0 % respectively using X-Ray fluorescence spectroscopy. The imaging by SEM and particle size distribution determined by PSD showed that the synthesized silica was in the agglomerate form which dimension of 7 and 9 μm. The specific surface area was found to be 775 and 660 m²/g, respectively. And the synthesized silica was modified with humic acids and characterized by Fourier transform infrared spectroscopy. The results showed that humic acids could be successfully coated on silica surface.