The purpose of this study was to demonstrate a facile method to produce monodispersed and size-controllable potassium silicate nanoparticles from rice straw waste. Different from other methods that use expensive raw chemicals, our method utilises rice straw waste as a source of silica that is cost-free and largely available. In the experimental procedure, rice straw waste was burned. Then, the burned rice straw waste was put into the alkaline extraction process (using potassium solution) and flame-assisted spray-pyrolysis apparatus system. To support the flame-assisted spray-pyrolysis, we utilised commercially available liquid petroleum gas as a fuel source for the flame combustion process. Experimental results showed that the prepared particles are monodispersed, spherical, and having sizes in the range of nanometer (from 20 to 80 nm). The fuel flow rate plays important role in controlling particle size in the final product. Increases in the fuel lead to the formation of larger particles. Since the present method can convert rice straw into useful and valuable potassium silica particles, further development of this study would give a positive impact for the reduction of rice straw waste emission.