The segmented flow technique is used for continuous synthesis of ZnO nanoparticles under micro reaction conditions. The experimental setup consisted of syringe pumps and T-type injectors, PTFE tubings as well as PTFE knot mixers in a thermostated bath. ZnO nanoparticles were obtained by generation under strong alkaline conditions and elevated temperature in aqueous solution and by precipitation under moderate alkaline conditions in DMSO solution. In aqueous solution, small compact nanoparticles (diameters below 100 nm) were obtained at high temperature (90°C) and high reactant concentrations. Larger crystals, nanoneedles and nanoflowers (submicron and lower micro range) were obtained at reduced concentrations and reduced temperature (70°C). Compact nanocrystals with diameters of a few hundred nanometers are formed by the reaction of zinc acetate with tetramethylammoniumhydroxide in the presence of polyethylene glycole (at 80°C). In nearly all cases, a strong effect of flow rate on nanoparticle quality was observed. Enhanced flow rates (up to 5000 μL/min) lead to an improvement of shape homogeneity and size distribution.