Carbon quantum dots (CQDs) have potential to replace metal-based quantum dots due to its low-toxicity. However, studies on CQDs preparation were dominated by synthetic carbon precursors. Switching the precursors into natural ingredient is preferred since they are highly abundant and low-cost. In this study, composite of silica-carbon quantum dots (Si-CQDs) were fabricated from rice husk through a hydrothermal process. Si-CQDs with diverse properties are beneficial for its application in the future; therefore, the variation of hydrothermal conditions (i.e., temperature and pH) was performed to investigate their influence on its properties. Investigation using HRTEM, XPS, Raman spectroscopy, and UV-Vis spectroscopy suggested that hydrothermal conditions affect carbonization reaction. Hydrothermal temperature controls carbonization rate of rice husk ash, while acid addition accelerates polymerization and base addition tends to cut more carbons into small particles. The photoluminescence (PL) analysis showed that the obtained Si-CQD samples have emission in the range of 469�552 nm with various intensities. The application of sole Si-CQDs was evaluated in methylene blue (MB) degradation under visible light irradiation. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.