In this work, CeO2 nanoparticles were synthesized hydrothermally with supercritical water using a tubular flow reactor with three different configurations and various flow rates of the feed solution and supercritical water, and the effects of the reactor configuration and the flow rates of the two streams on the size distributions of the synthesized nanoparticles were investigated. In addition, the flow and thermal fields in the reactors were calculated numerically under the experimental conditions using FLUENT software, where the numerical results for the flow and thermal fields were also verified by neutron radiography. Comparing the experimental results of nanoparticle synthesis with the numerical results, it was revealed that the size distributions of the synthesized nanoparticles could be explained well on the basis of the flow patterns and temperature distributions in the reactor, which depended on the reactor configuration and process conditions. (C) 2015 Elsevier B.V. All rights reserved.