The impact of the residence time (τ) in a microreactor on the relative extent of nucleation, crystal growth, and agglomeration processes, leading to remarkable differences in materials characteristics (see figure) by a novel in-line dispersion-precipitation (ILDP) method for the preparation of nanomaterials is reported. The tuning of crystallite size (D) and surface area (SBET) is illustrated for Mg-Al hydrotalcites (synthetic clays).