Herein, we report on an efficient strategy to synthesize anatase nanoparticles in a spiral microreactor. The synthesized nanopowders were characterized by X-ray diffraction and high resolution transmission electron microscopy. L-25(5(6)) orthogonal experiments were performed in order to assess the effect of each factor on the particle size of anatase nanopowders. Finally, the residence time R value was 50.734, which was much larger than R values for other factors, highlighting residence time as the key factor determining anatase nanoparticle size. (C) 2018 Elsevier B.V. All rights reserved.