Continuous flow synthesis of gold nanoparticles was demonstrated using a microchannel reactor with glucose reduction in aqueous alkaline medium. Particle size, morphology, and visual/optical properties of the dispersion liquid were controlled dynamically by tuning of the rate of NaOH addition. Characteristic star-like nanoparticles formed spontaneously as a quasi-stable state, but they changed the morphology to round shape and showed spectral change over time. (C) 2011 Elsevier Inc. All rights reserved.