Continuous synthesis of nickel nanoparticles was conducted in a microstructured reactor by chemical reduction of nickel chloride dissolved in ethanol by hydrazine hydrate. A novel vapor-liquid segmented flow method was thus developed based on partial vaporization of the ethanol in the reaction system, leading to formation of nickel nanoparticles in a smooth manner without clogging. The effect of the residence time, the reaction temperature and addition of surfactant was examined. Nickel nanoparticles with mean diameters of about 80 nm and narrow particle size distributions could be synthesized at 60-75 degrees C within 4 min. Addition of cetyltrimethylammonium bromide in the reaction system resulted in further decrease in the particle size to 68 nm. The nickel nanoparticles exhibit superior catalytic activities to the commercial used Raney Ni catalyst in hydrogenation of of p-nitrophenol to p-aminophenol. (C) 2012 Elsevier B.V. All rights reserved.