Conventional microreactors for nanoparticle synthesis were operated at low flow velocity as well as more residence time because of low mixing efficiency of the meander micromixer. Here, we purpose a simple obstacle micromixer to be operated at a wide range of flow velocity for increasing single-channel synthesis production rate of silica nanoparticles. Results show our obstacle micromixer has over 85% mixing efficiency covering the flow regions in both convection and diffusion mixing. This microreactor was used to synthesize silica nanoparticles with an average diameter of 200-250 nm. Enhancing fluid mixing at high flow velocity can result in high production rate.